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<?xml version="1.0" encoding="utf-8"?><feed xmlns="http://www.w3.org/2005/Atom" ><generator uri="https://jekyllrb.com/" version="3.8.5">Jekyll</generator><link href="https://csirmazbendeguz.net/feed.xml" rel="self" type="application/atom+xml" /><link href="https://csirmazbendeguz.net/" rel="alternate" type="text/html" /><updated>2021-06-20T01:35:08+01:00</updated><id>https://csirmazbendeguz.net/feed.xml</id><entry><title type="html">How to convert a matrix to a table in Google Sheets</title><link href="https://csirmazbendeguz.net/2021/06/19/how-to-convert-a-matrix-to-a-table-in-google-sheets.html" rel="alternate" type="text/html" title="How to convert a matrix to a table in Google Sheets" /><published>2021-06-19T00:00:00+01:00</published><updated>2021-06-19T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2021/06/19/how-to-convert-a-matrix-to-a-table-in-google-sheets</id><content type="html" xml:base="https://csirmazbendeguz.net/2021/06/19/how-to-convert-a-matrix-to-a-table-in-google-sheets.html">&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Motivation&lt;/h3&gt;
  &lt;p&gt;
    I came across an interesting problem while performing my data engineering duties at work.
  &lt;/p&gt;
  &lt;p&gt;
    I had to import a spreadsheet's content into a relational database.
    It may sound like a trivial task, but there was a catch: the data was defined in a matrix format.
  &lt;/p&gt;
  &lt;p&gt;
    It looked something like this:
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/matrix.png&quot;
        alt=&quot;The matrix&quot;
        title=&quot;The matrix&quot;
        style=&quot;max-width:900px;&quot;
    /&gt;
  &lt;/p&gt;
  &lt;p&gt;
    It's a matrix that defines the monthly budget of each department for the first half of 2021.
  &lt;/p&gt;
  &lt;p&gt;
    To import this data into an RDBMS, we need to convert it to a table first.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/expected.png&quot;
        alt=&quot;The table&quot;
        title=&quot;The table&quot;
        style=&quot;max-width:900px;max-height:500px;&quot;
    /&gt;
  &lt;/p&gt;
  &lt;p&gt;
    The transformation should be dynamic, so when the matrix is updated,
    the changes are automatically reflected in the table.
  &lt;/p&gt;
  &lt;p&gt;
    I haven't found any articles on the subject, so I think my solution is worth sharing.
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Helper tables&lt;/h3&gt;
  &lt;p&gt;
    To make our lives easier, let's define two helper tables - one for the matrix rows and one for the matrix columns.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/matrix-rows-table.png&quot;
        alt=&quot;The matrix rows table&quot;
        title=&quot;The matrix rows table&quot;
        style=&quot;max-width:400px;max-height:300px;margin: 12px;&quot;
    /&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/matrix-columns-table.png&quot;
        alt=&quot;The matrix columns table&quot;
        title=&quot;The matrix columns table&quot;
        style=&quot;max-width:300px;max-height:300px;margin: 12px;&quot;
    /&gt;
  &lt;/p&gt;
  &lt;p&gt;
    Let's make them truly dynamic, so whenever a new row or column is added to the matrix, it automatically appears in
    the helper table.
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Counting the matrix rows/columns&lt;/h3&gt;
  &lt;p&gt;First, we need a way to count the number of rows/columns in the matrix.&lt;/p&gt;
  &lt;p&gt;
    Luckily for us, the &lt;a href=&quot;https://support.google.com/docs/answer/3093991?hl=en-GB&quot;&gt;COUNTA&lt;/a&gt; function
    will cover 100% of our counting needs.
  &lt;/p&gt;
  &lt;p&gt;
    It's a function that counts all non-empty cells inside a given range:
  &lt;/p&gt;
  &lt;ul&gt;
    &lt;li&gt;
      &lt;code class=&quot;highlighter-rouge&quot;&gt;counta(matrix!$A:$A)&lt;/code&gt; - count the number of rows (i.e. non-empty cells in &lt;em&gt;column A&lt;/em&gt;)
    &lt;/li&gt;
    &lt;li&gt;
      &lt;code class=&quot;highlighter-rouge&quot;&gt;counta(matrix!$1:$1)&lt;/code&gt; - count the number of columns (i.e. non-empty cells in &lt;em&gt;row 1&lt;/em&gt;)
    &lt;/li&gt;
  &lt;/ul&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/count-items.png&quot;
        alt=&quot;Counting the matrix rows/columns&quot;
        title=&quot;Counting the matrix rows/columns&quot;
        style=&quot;max-width:600px;max-height:300px;&quot;
    /&gt;
  &lt;/p&gt;
  &lt;p&gt;In its current state, the matrix has 9 rows and 6 columns.&lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Copying the matrix rows&lt;/h3&gt;
  &lt;p&gt;
    To copy the matrix rows, we can use the
    &lt;a href=&quot;https://support.google.com/docs/answer/3093275?hl=en-GB&quot;&gt;ARRAYFORMULA&lt;/a&gt; function.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/copy-matrix-rows.png&quot;
        alt=&quot;Copying the matrix rows&quot;
        title=&quot;Copying the matrix rows&quot;
        style=&quot;max-width:600px;max-height:300px;&quot;
    /&gt;
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;ARRAYFORMULA(INDIRECT(&quot;matrix!A2:A&quot; &amp;amp; (COUNTA(matrix!$A:$A) + 1)))&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;
    This formula:
    &lt;ul&gt;
      &lt;li&gt;
        Builds the string &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;matrix!A2:A10&quot;&lt;/code&gt;.
        This string represents the cell range of the matrix rows.
      &lt;/li&gt;
      &lt;li&gt;
        If a new row is added to the matrix, the range is automatically increased by one row (because of the
        &lt;code class=&quot;highlighter-rouge&quot;&gt;COUNTA&lt;/code&gt; function).
      &lt;/li&gt;
      &lt;li&gt;
        Then, it converts the &lt;em&gt;cell range string&lt;/em&gt; to an actual &lt;em&gt;cell range reference&lt;/em&gt; with the
        &lt;a href=&quot;https://support.google.com/docs/answer/3093377?hl=en-GB&quot;&gt;INDIRECT&lt;/a&gt; function.
      &lt;/li&gt;
      &lt;li&gt;
        Finally, it copies the cell range reference to the current position with the &lt;em&gt;ARRAYFORMULA&lt;/em&gt; function.
      &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Generating ID numbers&lt;/h3&gt;
  &lt;p&gt;
    To generate ID numbers, we can use &lt;em&gt;ARRAYFORMULA&lt;/em&gt; combined with the
    &lt;a href=&quot;https://support.google.com/docs/answer/3093316?hl=en-GB&quot;&gt;ROW&lt;/a&gt; function.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/generating-id-numbers.png&quot;
        alt=&quot;Generating ID numbers&quot;
        title=&quot;Generating ID numbers&quot;
        style=&quot;max-width:600px;max-height:300px;&quot;
    /&gt;
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;ARRAYFORMULA(ROW(INDIRECT(&quot;B2:B&quot; &amp;amp; (COUNTA($B:$B)))) - 2)&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;
    The idea is similar to copying cells.
    &lt;ul&gt;
      &lt;li&gt;
        First, it builds the &lt;em&gt;cell range string&lt;/em&gt; &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;B2:B10&quot;&lt;/code&gt;.
        If a row is added/deleted, this range is automatically adjusted.
      &lt;/li&gt;
      &lt;li&gt;
        Then, it converts the string to a &lt;em&gt;cell range reference&lt;/em&gt; with &lt;em&gt;INDIRECT&lt;/em&gt;.
      &lt;/li&gt;
      &lt;li&gt;
        Next, it takes the row number of each cell (with &lt;em&gt;ROW&lt;/em&gt;) and subtracts two from all of them, so the
        resulting sequence is zero-based. We'll see why this is important later.
      &lt;/li&gt;
      &lt;li&gt;
        Finally, it copies the sequence to the given position with &lt;em&gt;ARRAYFORMULA&lt;/em&gt;.
      &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Calculating the last matrix column&lt;/h3&gt;
  &lt;p&gt;
    To calculate the last matrix column, we can use the
    &lt;a href=&quot;https://support.google.com/docs/answer/3093308?hl=en-GB&quot;&gt;ADDRESS&lt;/a&gt; function.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/getting-the-last-matrix-column.png&quot;
        alt=&quot;Calculating the last matrix column&quot;
        title=&quot;Calculating the last matrix column&quot;
        style=&quot;max-width:450px;max-height:250px;&quot;
    /&gt;
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;address(1, counta(matrix!$1:$1) + 1, 4)&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;
    The &lt;em&gt;ADDRESS&lt;/em&gt; function takes a row and a column number, and returns a cell reference string.
  &lt;/p&gt;
  &lt;p&gt;
    So, in the formula above:
    &lt;ul&gt;
      &lt;li&gt;
        &lt;code class=&quot;highlighter-rouge&quot;&gt;1&lt;/code&gt; is the row number.
      &lt;/li&gt;
      &lt;li&gt;
        &lt;code class=&quot;highlighter-rouge&quot;&gt;counta(matrix!$1:$1) + 1&lt;/code&gt; is the column number.
        It will evaluate to &lt;code class=&quot;highlighter-rouge&quot;&gt;7&lt;/code&gt; in this example.
        Column 7 is G.
      &lt;/li&gt;
      &lt;li&gt;
        &lt;code class=&quot;highlighter-rouge&quot;&gt;4&lt;/code&gt; is the flag for returning the address in the format
        &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;G1&quot;&lt;/code&gt;.
      &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Copying the matrix columns&lt;/h3&gt;
  &lt;p&gt;
    Copying the matrix columns is pretty similar to copying the rows.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/copy-matrix-columns.png&quot;
        alt=&quot;Copying the matrix columns&quot;
        title=&quot;Copying the matrix columns&quot;
        style=&quot;max-width:700px;max-height:400px;&quot;
    /&gt;
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;transpose(arrayformula(to_text(indirect(&quot;matrix!B1:&quot; &amp;amp; address(1, counta(matrix!$1:$1) + 1, 4)))))&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;That's quite a mouthful! Here's what it does:&lt;/p&gt;
  &lt;p&gt;
    &lt;ul&gt;
      &lt;li&gt;
        First, it builds the &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;matrix!B1:G1&quot;&lt;/code&gt; cell range string with the help
        of the &lt;em&gt;ADDRESS&lt;/em&gt; function.
      &lt;/li&gt;
      &lt;li&gt;
        If a new column is added, the range is automatically adjusted.
        For example, if we added the column &lt;code class=&quot;highlighter-rouge&quot;&gt;Jul-21&lt;/code&gt;, the cell range string would be
        &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;matrix!B1:H1&quot;&lt;/code&gt;
      &lt;/li&gt;
      &lt;li&gt;
        Then, it transforms the &lt;em&gt;cell range string&lt;/em&gt; to a &lt;em&gt;cell range reference&lt;/em&gt;
        with &lt;em&gt;INDIRECT&lt;/em&gt;, and copies the values to the position with
        &lt;em&gt;ARRAYFORMULA&lt;/em&gt; (as discussed above).
      &lt;/li&gt;
      &lt;li&gt;
        To make sure Google Sheets handles the values as texts (not as dates), all values are
        converted to text with the
        &lt;a href=&quot;https://support.google.com/docs/answer/3094285?hl=en-GB&quot;&gt;TO_TEXT&lt;/a&gt; function.
      &lt;/li&gt;
      &lt;li&gt;
        Note that &lt;em&gt;ARRAYFORMULA&lt;/em&gt; will output the cell range horizontally.
        To change it to vertical, we need to use the
        &lt;a href=&quot;https://support.google.com/docs/answer/3094262?hl=en-GB&quot;&gt;TRANSPOSE&lt;/a&gt; function.
      &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Flattening the matrix values&lt;/h3&gt;
  &lt;p&gt;Now that both helper tables are ready, we can start adding columns to the main table.&lt;/p&gt;
  &lt;p&gt;
    To make things easier, let's use the
    &lt;a href=&quot;https://support.google.com/docs/answer/10307761?hl=en-GB&quot;&gt;FLATTEN&lt;/a&gt; function.
  &lt;/p&gt;
  &lt;p&gt;
    The &lt;em&gt;FLATTEN&lt;/em&gt; function takes a range of values and &lt;em&gt;flattens&lt;/em&gt; them into a single column.
  &lt;/p&gt;
  &lt;p&gt;
    For example:
  &lt;/p&gt;
  &lt;div style=&quot;text-align: center;&quot;&gt;
    &lt;table style=&quot;display: inline-block; vertical-align: middle;&quot;&gt;
      &lt;tr&gt;
        &lt;td&gt;0&lt;/td&gt;
        &lt;td&gt;1&lt;/td&gt;
        &lt;td&gt;2&lt;/td&gt;
        &lt;td&gt;3&lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td&gt;4&lt;/td&gt;
        &lt;td&gt;5&lt;/td&gt;
        &lt;td&gt;6&lt;/td&gt;
        &lt;td&gt;7&lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td&gt;8&lt;/td&gt;
        &lt;td&gt;9&lt;/td&gt;
        &lt;td&gt;10&lt;/td&gt;
        &lt;td&gt;11&lt;/td&gt;
      &lt;/tr&gt;
    &lt;/table&gt;
    &lt;div style=&quot;display: inline-block; vertical-align: middle;&quot;&gt;&amp;#8594;&lt;/div&gt;
    &lt;table style=&quot;display: inline-block; vertical-align: middle;&quot;&gt;
      &lt;tr&gt;&lt;td&gt;0&lt;/td&gt;&lt;/tr&gt;
      &lt;tr&gt;&lt;td&gt;1&lt;/td&gt;&lt;/tr&gt;
      &lt;tr&gt;&lt;td&gt;...&lt;/td&gt;&lt;/tr&gt;
      &lt;tr&gt;&lt;td&gt;11&lt;/td&gt;&lt;/tr&gt;
    &lt;/table&gt;
  &lt;/div&gt;
  &lt;p&gt;
    We can use it to extract the matrix values into the main table:
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/flattening-matrix-values.png&quot;
        alt=&quot;Flattening the matrix values&quot;
        title=&quot;Flattening the matrix values&quot;
        style=&quot;max-width:700px;max-height:400px;&quot;
    /&gt;
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;flatten(indirect(&quot;matrix!B2:&quot; &amp;amp; address(counta(matrix!$A:$A) + 1, counta(matrix!$1:$1) + 1, 4)))&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;
    Conceptually, this formula is pretty similar to the previous ones:
  &lt;/p&gt;
  &lt;p&gt;
    &lt;ul&gt;
      &lt;li&gt;
        First, it builds the &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;matrix!B2:G10&quot;&lt;/code&gt; cell range string with the
        help of the &lt;em&gt;ADDRESS&lt;/em&gt; function.
        This range includes all matrix values (but not the row/column names).
        If someone adds a new column or row to the matrix, it is automatically adjusted.
      &lt;/li&gt;
      &lt;li&gt;
        Then, the &lt;em&gt;cell range string&lt;/em&gt; is transformed to a &lt;em&gt;cell range reference&lt;/em&gt; with &lt;em&gt;INDIRECT&lt;/em&gt;.
      &lt;/li&gt;
      &lt;li&gt;
        Finally, &lt;em&gt;FLATTEN&lt;/em&gt; flattens the matrix values into a column and outputs them
        (similarly to &lt;em&gt;ARRAYFORMULA&lt;/em&gt;).
      &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/p&gt;
  &lt;aside class=&quot;comment&quot;&gt;
    &lt;p&gt;
      Note that &lt;em&gt;FLATTEN&lt;/em&gt; transforms the values in a &lt;strong&gt;left-to-right then top-to-bottom order&lt;/strong&gt;.
    &lt;/p&gt;
    &lt;p&gt;
      This is good news - &lt;u&gt;we can exploit the ordering to calculate the corresponding rows/columns&lt;/u&gt;.
    &lt;/p&gt;
  &lt;/aside&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Calculating the row IDs&lt;/h3&gt;
  &lt;p&gt;
    To calculate which matrix row a given item belongs to, divide the ID with the width of the matrix
    and discard the remainder (keep the integer part only).
  &lt;/p&gt;
  &lt;p&gt;
    For example:
  &lt;/p&gt;
  &lt;table&gt;
    &lt;tr&gt;
      &lt;td&gt;0&lt;/td&gt;
      &lt;td&gt;1&lt;/td&gt;
      &lt;td&gt;2&lt;/td&gt;
      &lt;td&gt;3&lt;/td&gt;
      &lt;td&gt;&amp;#8594;&lt;/td&gt;
      &lt;td&gt;0&lt;/td&gt;

    &lt;/tr&gt;
    &lt;tr&gt;
      &lt;td&gt;4&lt;/td&gt;
      &lt;td&gt;5&lt;/td&gt;
      &lt;td&gt;6&lt;/td&gt;
      &lt;td&gt;7&lt;/td&gt;
      &lt;td&gt;&amp;#8594;&lt;/td&gt;
      &lt;td&gt;1&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
      &lt;td&gt;8&lt;/td&gt;
      &lt;td&gt;9&lt;/td&gt;
      &lt;td&gt;10&lt;/td&gt;
      &lt;td&gt;11&lt;/td&gt;
      &lt;td&gt;&amp;#8594;&lt;/td&gt;
      &lt;td&gt;2&lt;/td&gt;
    &lt;/tr&gt;
  &lt;/table&gt;
  &lt;p&gt;
    That is,
    &lt;ul&gt;
      &lt;li&gt;0, 1, 2 and 3 divided by 4 is 0&lt;/li&gt;
      &lt;li&gt;4, 5, 6 and 7 divided by 4 is 1&lt;/li&gt;
      &lt;li&gt;8, 9, 10 and 11 divided by 4 is 2&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/p&gt;
  &lt;p&gt;
    The
    &lt;a href=&quot;https://support.google.com/docs/answer/3093436?hl=en-GB&quot;&gt;QUOTIENT&lt;/a&gt;
    function is the natural choice for this calculation.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/calculating-row-ids.png&quot;
        alt=&quot;Calculating the row IDs&quot;
        title=&quot;Calculating the row IDs&quot;
        style=&quot;max-width:700px;max-height:400px;&quot;
    /&gt;
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;ARRAYFORMULA(QUOTIENT(INDIRECT(&quot;A2:A&quot; &amp;amp; COUNTA($A:$A)), COUNTA(matrix!$1:$1)))&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;The formula is pretty straightforward:&lt;/p&gt;
  &lt;p&gt;
  &lt;ul&gt;
    &lt;li&gt;
      First, it builds the &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;A2:A55&quot;&lt;/code&gt; cell range string (referring to
      the &lt;strong&gt;id&lt;/strong&gt; column) and
      creates a cell range reference with the &lt;em&gt;INDIRECT&lt;/em&gt; function.
    &lt;/li&gt;
    &lt;li&gt;
      Then, the values are transformed with the &lt;em&gt;QUOTIENT&lt;/em&gt; function
      (according to the rules above).
    &lt;/li&gt;
    &lt;li&gt;
      Finally, the values are copied to the given cell with &lt;em&gt;ARRAYFORMULA&lt;/em&gt;.
    &lt;/li&gt;
  &lt;/ul&gt;
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Calculating the column IDs&lt;/h3&gt;
  &lt;p&gt;
    To calculate which matrix column a given item belongs to, divide the ID with the width of the matrix
    and discard the integer part (keep the remainder only).
  &lt;/p&gt;
  &lt;p&gt;
    For example:
  &lt;/p&gt;
  &lt;table&gt;
    &lt;tr&gt;
      &lt;td&gt;0&lt;/td&gt;
      &lt;td&gt;1&lt;/td&gt;
      &lt;td&gt;2&lt;/td&gt;
      &lt;td&gt;3&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
      &lt;td&gt;4&lt;/td&gt;
      &lt;td&gt;5&lt;/td&gt;
      &lt;td&gt;6&lt;/td&gt;
      &lt;td&gt;7&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
      &lt;td&gt;8&lt;/td&gt;
      &lt;td&gt;9&lt;/td&gt;
      &lt;td&gt;10&lt;/td&gt;
      &lt;td&gt;11&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
      &lt;td&gt;&amp;#8595;&lt;/td&gt;
      &lt;td&gt;&amp;#8595;&lt;/td&gt;
      &lt;td&gt;&amp;#8595;&lt;/td&gt;
      &lt;td&gt;&amp;#8595;&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
      &lt;td&gt;0&lt;/td&gt;
      &lt;td&gt;1&lt;/td&gt;
      &lt;td&gt;2&lt;/td&gt;
      &lt;td&gt;3&lt;/td&gt;
    &lt;/tr&gt;
  &lt;/table&gt;
  &lt;p&gt;
    That is,
    &lt;ul&gt;
      &lt;li&gt;0, 4 and 8 modulo 4 is 0&lt;/li&gt;
      &lt;li&gt;1, 5 and 9 modulo 4 is 1&lt;/li&gt;
      &lt;li&gt;2, 6 and 10 modulo 4 is 2&lt;/li&gt;
      &lt;li&gt;3, 7 and 11 modulo 4 is 3&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/p&gt;
  &lt;p&gt;
    For this calculation,
    the appropriate function is
    &lt;a href=&quot;https://support.google.com/docs/answer/3093497?hl=en-GB&quot;&gt;MOD&lt;/a&gt;.
  &lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/calculating-column-ids.png&quot;
        alt=&quot;Calculating the column IDs&quot;
        title=&quot;Calculating the column IDs&quot;
        style=&quot;max-width:700px;max-height:400px;&quot;
    /&gt;
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;ARRAYFORMULA(MOD(INDIRECT(&quot;A2:A&quot; &amp;amp; COUNTA($A:$A)), COUNTA(matrix!$1:$1)))&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Looking up the rows/columns by their IDs&lt;/h3&gt;
  &lt;p&gt;
    We're almost done!
  &lt;/p&gt;
  &lt;p&gt;
    We already have the row and column IDs.
    All that's left to do is to &lt;em&gt;look up&lt;/em&gt; the actual values from the helper tables...
    and when it comes to looking up things, the best in the business is:
    &lt;a href=&quot;https://support.google.com/docs/answer/3093318?hl=en-GB&quot;&gt;VLOOKUP&lt;/a&gt;.
  &lt;/p&gt;
  &lt;p&gt;
    To put it simply, it's a function for performing a linear search in a table.
    For example:
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;VLOOKUP(0, rows!A2:B10, 2) --&amp;gt; &quot;Business Development&quot;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;Translates to: &quot;find the row name where the id is 0&quot;.&lt;/p&gt;
  &lt;p&gt;
    The function takes 3 parameters:
  &lt;/p&gt;
  &lt;ul&gt;
    &lt;li&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;0&lt;/code&gt; - the id to search for&lt;/li&gt;
    &lt;li&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;rows!A2:B10&lt;/code&gt; - the table to search in&lt;/li&gt;
    &lt;li&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;2&lt;/code&gt; - the column to return&lt;/li&gt;
  &lt;/ul&gt;
  &lt;p&gt;And it can also be combined with &lt;em&gt;ARRAYFORMULA&lt;/em&gt;:&lt;/p&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/looking-up-rows.png&quot;
        alt=&quot;Looking up rows&quot;
        title=&quot;Looking up rows&quot;
        style=&quot;max-width:700px;max-height:400px;&quot;
    /&gt;
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;ARRAYFORMULA(VLOOKUP(INDIRECT(&quot;C2:C&quot; &amp;amp; COUNTA($C:$C)), INDIRECT(&quot;rows!A2:B&quot; &amp;amp; COUNTA(rows!$B:$B)), 2))&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;
    It looks a bit complicated, but there's actually nothing new here:
  &lt;/p&gt;
  &lt;ul&gt;
    &lt;li&gt;
      First, it builds the &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;C2:C55&quot;&lt;/code&gt; and
      &lt;code class=&quot;highlighter-rouge&quot;&gt;&quot;rows!A2:B10&quot;&lt;/code&gt; cell range references.
      The first one refers to the &lt;strong&gt;row id&lt;/strong&gt; column, the second one refers to the rows helper table.
    &lt;/li&gt;
    &lt;li&gt;
      We pass 3 arguments to &lt;em&gt;VLOOKUP&lt;/em&gt; - the ids to search for, the table to search
      in and the column to return.
    &lt;/li&gt;
    &lt;li&gt;
      Finally, &lt;em&gt;VLOOKUP&lt;/em&gt; finds the row name for each id and the results are displayed with &lt;em&gt;ARRAYFORMULA&lt;/em&gt;.
    &lt;/li&gt;
  &lt;/ul&gt;
  &lt;p style=&quot;text-align:center;margin:18px 0;&quot;&gt;
    &lt;img
        src=&quot;/assets/images/how-to-convert-a-matrix-to-a-table-in-google-sheets/looking-up-columns.png&quot;
        alt=&quot;Looking up columns&quot;
        title=&quot;Looking up columns&quot;
        style=&quot;max-width:700px;max-height:400px;&quot;
    /&gt;
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-escape&quot; data-lang=&quot;escape&quot;&gt;ARRAYFORMULA(VLOOKUP(INDIRECT(&quot;D2:D&quot; &amp;amp; COUNTA($D:$D)), INDIRECT(&quot;columns!A2:B&quot; &amp;amp; COUNTA(columns!$B:$B)), 2))&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Conclusion&lt;/h3&gt;
  &lt;p&gt;
    That's it!
  &lt;/p&gt;
  &lt;p&gt;
    We transformed a matrix into a table using nothing but Google Sheets formulas.
    Not as easy as it looks!
  &lt;/p&gt;
  &lt;p&gt;
    I hope this post was helpful.
  &lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author></entry><entry><title type="html">I wanna be the very best</title><link href="https://csirmazbendeguz.net/2020/12/21/i-wanna-be-the-very-best.html" rel="alternate" type="text/html" title="I wanna be the very best" /><published>2020-12-21T00:00:00+00:00</published><updated>2020-12-21T00:00:00+00:00</updated><id>https://csirmazbendeguz.net/2020/12/21/i-wanna-be-the-very-best</id><content type="html" xml:base="https://csirmazbendeguz.net/2020/12/21/i-wanna-be-the-very-best.html">&lt;section class=&quot;section&quot;&gt;
    &lt;p style=&quot;text-align:center;&quot;&gt;
        &lt;img
            src=&quot;/assets/images/i-wanna-be-the-very-best/memgame.png&quot;
            alt=&quot;A screenshot of the game&quot;
            title=&quot;A screenshot of the game&quot;/&gt;
    &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Motivation&lt;/h3&gt;
    &lt;p&gt;
        My favorite course in school was Java development. It opened a whole new world for me.
    &lt;/p&gt;
    &lt;p&gt;
        I have learned other programming languages before, but Java was the first one I actually &lt;s&gt;mastered&lt;/s&gt; tried to master.
        It solidifed my programming skills, and more importantly, it enabled me to build applications for virtually any platform.
    &lt;/p&gt;
    &lt;p&gt;
        Yes! I'm talking about &lt;strong&gt;video games&lt;/strong&gt;, for desktop. Go figure!
    &lt;/p&gt;
    &lt;p&gt;
        Luckily for me, the curriculum included GUI programming. They taught us &lt;em&gt;Java Swing&lt;/em&gt;, an old graphics library from the 90s.
        I particularly enjoyed one of the assignments: we had to build a memory game (also called &quot;&lt;em&gt;concentration&lt;/em&gt;&quot; - as I've learned lately).
    &lt;/p&gt;
    &lt;p&gt;
        Apart from a few loose requirements, we were given the freedom to implement the game in whatever way we saw fit.
        As a recovering Pokémon-addict (grew up watching the series), there was no question about what theme I will choose.
    &lt;/p&gt;
    &lt;p&gt;
        I built the game as well as I could. I even photoshopped artwork (that I got from the internet) to make it as perfect as possible.
        I received the best possible grade and was so proud I eventually also uploaded it to GitHub - so the whole world can see my fine work.
    &lt;/p&gt;
    &lt;p&gt;This was in 2016...&lt;/p&gt;
    &lt;p&gt;
        In 2019 I decided to revisit my old GitHub repositories. Why?
        Because for software developers, GitHub is like a portfolio.
        And you don't want shitty projects on your portfolio.
    &lt;/p&gt;
    &lt;p&gt;
        What I found there was staggering: past me had no idea how to develop good software.
        Despite all the love I put into this game, it was a dumpster fire.
    &lt;/p&gt;
    &lt;p&gt;
        I ended up making most of my old repositories private, except this one. I decided to save it.
    &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;The bane of GUI programming&lt;/h3&gt;
    &lt;p&gt;
        The codebase was a textbook example of bad practices.
    &lt;/p&gt;
    &lt;p&gt;
        It was full of duplications, everything was hardcoded, and for some reason I thought committing executable files to Git was a good idea.
        Fortunately, I managed to fix the obvious problems quite quickly.
    &lt;/p&gt;
    &lt;p&gt;
        The the challenging part was not replacing tabs with spaces or renaming variables.
        It was the architecture.
    &lt;/p&gt;
    &lt;p&gt;
        Java Swing is a GUI library with basic GUI components like buttons, labels, panels, etc.
    &lt;/p&gt;
    &lt;p style=&quot;text-align:center;&quot;&gt;
        &lt;img src=&quot;/assets/images/i-wanna-be-the-very-best/memgame-components.png&quot;
             alt=&quot;A screenshot with the game's graphical components highlighted&quot;
             title=&quot;A screenshot with the game's graphical components highlighted&quot;/&gt;
    &lt;/p&gt;
    &lt;p&gt;
        There aren't many restrictions on how to organize code. The library doesn't care how you wire the components together.
        It is the programmer's job to come up with a sufficiently decoupled and modularized architecture.
    &lt;/p&gt;
    &lt;p&gt;
    In my opinion, anyone building an app with this toolkit will face the following two problems:
        &lt;ul&gt;
            &lt;li&gt;How do I make components talk to each other?&lt;/li&gt;
            &lt;li&gt;How do I avoid tight coupling?&lt;/li&gt;
        &lt;/ul&gt;
    &lt;/p&gt;
    &lt;p&gt;
        These are not easy problems. No wonder I couldn't tackle them when I was a beginner.
        After doing some research I decided on the following solutions...
    &lt;/p&gt;
&lt;/section&gt;


&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Inversion of Control&lt;/h3&gt;
    &lt;p&gt;
        Let's say, the user restarts the game by clicking the restart button.
    &lt;/p&gt;
    &lt;p&gt;
        We expect the following things to happen:
        &lt;ul&gt;
            &lt;li&gt;The board resets the memory cards.&lt;/li&gt;
            &lt;li&gt;The timer resets to zero.&lt;/li&gt;
            &lt;li&gt;The move counter resets to zero.&lt;/li&gt;
        &lt;/ul&gt;
    &lt;/p&gt;
    &lt;p&gt;That's &lt;strong&gt;a lot&lt;/strong&gt; of responsibilities for a single button!&lt;/p&gt;
    &lt;p&gt;A naive solution would look something like this:&lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-java&quot; data-lang=&quot;java&quot;&gt;&lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;RestartButton&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JButton&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;implements&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ActionListener&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;kd&quot;&gt;private&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;BoardPanel&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;boardPanel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;
    &lt;span class=&quot;kd&quot;&gt;private&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;TimerLabel&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;timerLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;
    &lt;span class=&quot;kd&quot;&gt;private&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;TriesLabel&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;triesLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;

    &lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;RestartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;BoardPanel&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;boardPanel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;TimerLabel&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;timerLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;TriesLabel&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;triesLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;kd&quot;&gt;super&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;Restart&quot;&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;);&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;this&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;boardPanel&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;boardPanel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;this&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;timerLabel&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;timerLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;this&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;triesLabel&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;triesLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;

    &lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;void&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;actionPerformed&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;ActionEvent&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;e&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;boardPanel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;reset&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;();&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;timerLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;reset&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;();&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;triesLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;reset&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;();&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
    &lt;p&gt;The problem with this approach is, the restart button should not communicate with other components directly.&lt;/p&gt;
    &lt;p&gt;
        It should not keep track of components handling game restarts, and it should not know how to call them.
        That's not the button's responsibility.
    &lt;/p&gt;
    &lt;p&gt;
        In other words, we should be able to add new objects handling game restarts without modifying the restart button itself.
    &lt;/p&gt;
    &lt;p&gt;To achieve this, we need to introduce a new layer of abstraction. We need &lt;strong&gt;inversion of control&lt;/strong&gt;.&lt;/p&gt;
&lt;/section&gt;


&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Event Bus&lt;/h3&gt;
    &lt;p&gt;An event bus is a design pattern for building event-driven systems. It's pretty simple.&lt;/p&gt;
    &lt;p style=&quot;text-align:center;&quot;&gt;
        &lt;img src=&quot;/assets/images/i-wanna-be-the-very-best/crazybus.jpg&quot;
             alt=&quot;A flying bus&quot;
             title=&quot;A flying bus&quot;/&gt;
    &lt;/p&gt;
    &lt;p&gt;
        An event bus is a central object where you register all your event handlers (e.g. the timer component).
        Then, when an event is created (e.g. the restart button is clicked), it is broadcasted to all the registered handlers.
    &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-java&quot; data-lang=&quot;java&quot;&gt;&lt;span class=&quot;c1&quot;&gt;// RestartButton.java&lt;/span&gt;
&lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;RestartButton&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JButton&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;implements&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ActionListener&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;kd&quot;&gt;private&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;EventBus&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;

    &lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;RestartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;EventBus&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;kd&quot;&gt;super&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;Restart&quot;&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;);&lt;/span&gt;
        &lt;span class=&quot;k&quot;&gt;this&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;eventBus&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;;&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;

    &lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;void&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;actionPerformed&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;ActionEvent&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;e&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;dispatch&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;new&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;RestartEvent&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;());&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// TimerLabel.java&lt;/span&gt;
&lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;TimerLabel&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JLabel&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;implements&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;RestartListener&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;TimerLabel&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;EventBus&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;register&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;RestartListener&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;na&quot;&gt;class&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;this&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;);&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;

    &lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;void&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;restarted&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;RestartEvent&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;event&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;// Reset timer.&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
    &lt;p&gt;
        Much better! The components do not depend on each other anymore.
        They communicate via the event bus.
    &lt;/p&gt;
    &lt;p&gt;
        How can the event bus figure out where to send the events?
        I'll spare you the details, but the answer is: &lt;em&gt;reflection&lt;/em&gt; - if you're interested in the inner workings of the event system (I'm simplifying things a bit here), feel free to check out the &lt;a href=&quot;https://github.com/csirmazbendeguz/pokemon-memory-game&quot;&gt;source code&lt;/a&gt;.
    &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Decoupling with Dependency Injection&lt;/h3&gt;
    &lt;p&gt;
        In Java Swing, GUI components are defined in Java code, forming a tree-like structure.
    &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-java&quot; data-lang=&quot;java&quot;&gt;&lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JPanel&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;// ...&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;// Add children.&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;add&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;new&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;RestartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;());&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;add&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;new&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ChangeDimensionButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;());&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
    &lt;p&gt;
        The problem is, what if we have to change something at the bottom of the tree?
        Let's say, add the event bus to the restart button?
    &lt;/p&gt;
    &lt;p&gt;
        Well... we would have to pass the event bus to every component in the hierarchy.
        Even where it's not needed.
    &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-java&quot; data-lang=&quot;java&quot;&gt;&lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JPanel&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;EventBus&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;add&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;new&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;RestartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;));&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;add&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;new&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ChangeDimensionButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;());&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
    &lt;p&gt;
        It's a bit inconvenient. Also, it'll be hard to test (we want to write tests... right?).
    &lt;/p&gt;
    &lt;p&gt;
        In this case, the panel container doesn't need to know how to instantiate its child objects.
        Let's make our lives a little easier and use &lt;strong&gt;dependency injection&lt;/strong&gt;.
    &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-java&quot; data-lang=&quot;java&quot;&gt;&lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JPanel&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;RestartButton&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;restartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ChangeDimensionButton&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;changeDimensionButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;add&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;restartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;);&lt;/span&gt;
        &lt;span class=&quot;n&quot;&gt;add&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;changeDimensionButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;);&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
    &lt;p&gt;
        Great! We have pushed the responsibility of instantiating the child components one layer up in the hierarchy.
    &lt;/p&gt;
    &lt;p&gt;Like squeezing a toothpaste. We are making files slimmer by moving the complexity somewhere else.&lt;/p&gt;
    &lt;p style=&quot;text-align:center;&quot;&gt;
        &lt;img src=&quot;/assets/images/i-wanna-be-the-very-best/toothpaste.jpg&quot;
             alt=&quot;A squeezed toothpaste&quot;
             title=&quot;A squeezed toothpaste&quot;/&gt;
    &lt;/p&gt;
    &lt;p&gt;
        That sounds fantastic, but... when does it ever end? Will we have to instantiate everything at startup time? Yes. Kind of.
    &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Enter dependency injection frameworks!&lt;/h3&gt;
    &lt;p&gt;To make the project as over-engineered as possible (gotta show off those skills!), I decided to use a framework that automatically instantiates and injects objects on demand.&lt;/p&gt;
    &lt;p&gt;I picked &lt;a href=&quot;https://github.com/google/guice&quot;&gt;Guice&lt;/a&gt;.&lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-java&quot; data-lang=&quot;java&quot;&gt;&lt;span class=&quot;c1&quot;&gt;// EventBus.java&lt;/span&gt;
&lt;span class=&quot;nd&quot;&gt;@Singleton&lt;/span&gt;
&lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;EventBus&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;c1&quot;&gt;// ...&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// RestartButton.java&lt;/span&gt;
&lt;span class=&quot;nd&quot;&gt;@Singleton&lt;/span&gt;
&lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;RestartButton&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JButton&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;implements&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ActionListener&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nd&quot;&gt;@Inject&lt;/span&gt;
    &lt;span class=&quot;kd&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;RestartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;EventBus&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;eventBus&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;//  ...&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// Buttons.java&lt;/span&gt;
&lt;span class=&quot;nd&quot;&gt;@Singleton&lt;/span&gt;
&lt;span class=&quot;kd&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt; &lt;span class=&quot;kd&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;JPanel&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;nd&quot;&gt;@Inject&lt;/span&gt;
    &lt;span class=&quot;nc&quot;&gt;Buttons&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nc&quot;&gt;RestartButton&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;restartButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ChangeDimensionButton&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;changeDimensionButton&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;{&lt;/span&gt;
        &lt;span class=&quot;c1&quot;&gt;// ...&lt;/span&gt;
    &lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;o&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
    &lt;p&gt;
        Marvelous! Guice can handle the creation and wiring of most GUI components out of the box. All you have to do is define some annotations.
        Naturally, for dynamically generated components (e.g. the memory cards), we'll have to keep using &quot;new&quot;.
    &lt;/p&gt;
    &lt;p&gt;
        It's also possible to go a bit further with reflection, and auto-discover/auto-register event handlers on startup.
        In hindsight, I'm not sure it was my brightest idea - but it's definitely possible! The sky is the limit.
    &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Conclusion&lt;/h3&gt;
    &lt;p&gt;
        We have covered a lot of ground.
        There's certainly a difference between understanding event-driven systems and dependency injection and making them work.
        But, when it comes to these kind of apps, I believe it's the way to go.
    &lt;/p&gt;
    &lt;p&gt;I implemented the game in 1-2 weeks. Then I spent 1-2 months refactoring and polishing it.&lt;/p&gt;
    &lt;p&gt;I'm not complaining, it was a fun intellectual exercise and learning experience.&lt;/p&gt;

    &lt;p&gt;The game can be downloaded from the &lt;a href=&quot;https://github.com/csirmazbendeguz/pokemon-memory-game/releases&quot;&gt;releases page&lt;/a&gt; (requires Java 8).&lt;/p&gt;
    &lt;p&gt;Thanks for reading!&lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">What I learned from (re)writing a Pokémon-themed memory game</summary></entry><entry><title type="html">What programming language should I learn?</title><link href="https://csirmazbendeguz.net/2020/12/12/what-programming-language-should-i-learn.html" rel="alternate" type="text/html" title="What programming language should I learn?" /><published>2020-12-12T00:00:00+00:00</published><updated>2020-12-12T00:00:00+00:00</updated><id>https://csirmazbendeguz.net/2020/12/12/what-programming-language-should-i-learn</id><content type="html" xml:base="https://csirmazbendeguz.net/2020/12/12/what-programming-language-should-i-learn.html">&lt;section class=&quot;section&quot;&gt;
    &lt;p&gt;The long answer is: it depends.&lt;/p&gt;
    &lt;p&gt;The short answer is: JavaScript.&lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Let me explain...&lt;/h3&gt;

    &lt;p&gt;
        I think most developers are familiar with the long answer: it depends on what you want to build.
        Obviously. If the person has an interest in a specific platform the answer is trivial.
        Unfortunately, that's usually not the case.
    &lt;/p&gt;

    &lt;p&gt;The question is not: &lt;em&gt;&quot;What programming language should I learn to build apps for Android?&quot;&lt;/em&gt;.&lt;/p&gt;

    &lt;p&gt;The question is (rephrased): &lt;em&gt;&quot;What programming language should I learn to get a job in software development?&quot;&lt;/em&gt;.&lt;/p&gt;
    &lt;p&gt;And I think that's an entirely valid question to ask! And maybe more relevant than ever.&lt;/p&gt;

    &lt;p&gt;In my opinion, the best way to switch careers into IT is with &lt;strong&gt;front-end web development&lt;/strong&gt;.&lt;/p&gt;

    &lt;aside class=&quot;comment&quot;&gt;
        &lt;p&gt;Disclaimer: I've never actually worked as a front-end developer, nor have I switched careers, so you should take my advice with a grain of salt.&lt;/p&gt;
    &lt;/aside&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Why JavaScript?&lt;/h3&gt;
    &lt;ul&gt;
        &lt;li&gt;It's ubiquitous. JavaScript has a monopoly over the browsers, it's pretty much impossible to avoid. Every dev knows at least a little JS (even me!). Give in! :D&lt;/li&gt;
        &lt;li&gt;Career opportunities. From small agencies to Big Tech. There's also freelancing. A person who can build beautiful web user interfaces is an asset to any software company.&lt;/li&gt;
        &lt;li&gt;Lenient requirements. A lot of front-end professionals are self-taught, and I think, in general, the job requirements for front-end positions are a bit more lenient when it comes to formal education. Be prepared to get grilled on your portfolio instead!&lt;/li&gt;
        &lt;li&gt;It's visual. It means you get quick feedback if you're doing something right or wrong. Also, it can be a lot of fun.&lt;/li&gt;
    &lt;/ul&gt;

    &lt;p&gt;Are there any cons? Yes.&lt;/p&gt;
    &lt;p&gt;JavaScript (and scripting languages in general) might not be the best for learning programming fundamentals.&lt;/p&gt;
    &lt;p&gt;When I started out with PHP, object-oriented programming was a confusing mystery to me. It only started to make sense when I learned Java.&lt;/p&gt;

    &lt;p&gt;Still, if you're looking for a solid career path, I think JavaScript development is a great one.&lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">The age old question. I've been asked this multiple times recently, here are my thoughts.</summary></entry><entry><title type="html">Requests Session for OAuth 2 Client Credentials Flow with Authlib</title><link href="https://csirmazbendeguz.net/2020/04/04/oauth2-client-credentials-with-authlib.html" rel="alternate" type="text/html" title="Requests Session for OAuth 2 Client Credentials Flow with Authlib" /><published>2020-04-04T00:00:00+01:00</published><updated>2020-04-04T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2020/04/04/oauth2-client-credentials-with-authlib</id><content type="html" xml:base="https://csirmazbendeguz.net/2020/04/04/oauth2-client-credentials-with-authlib.html">&lt;section class=&quot;section&quot;&gt;
    &lt;h3&gt;Session&lt;/h3&gt;
    &lt;p&gt;The trick is using a Session object.&lt;/p&gt;
    &lt;p&gt;In Requests, Session objects allow you to abstract away things that are common to your API calls (such as authorization).&lt;/p&gt;
    &lt;p&gt;Luckily for us, &lt;a href=&quot;https://docs.authlib.org&quot;&gt;Authlib&lt;/a&gt; comes with its own OAuth2Session class included.&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-python&quot; data-lang=&quot;python&quot;&gt;&lt;span class=&quot;kn&quot;&gt;from&lt;/span&gt; &lt;span class=&quot;nn&quot;&gt;authlib.integrations.requests_client&lt;/span&gt; &lt;span class=&quot;kn&quot;&gt;import&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;OAuth2Session&lt;/span&gt;

&lt;span class=&quot;n&quot;&gt;session&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;OAuth2Session&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;client_id&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&amp;lt;client id&amp;gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;client_secret&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&amp;lt;client secret&amp;gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;token_endpoint_auth_method&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;client_secret_post&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;scope&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&amp;lt;scope 1&amp;gt; &amp;lt;scope 2&amp;gt; etc.&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;token_endpoint&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&amp;lt;token endpoint&amp;gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;grant_type&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;client_credentials&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt;
    &lt;span class=&quot;n&quot;&gt;token&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;=&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;access_token&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;bp&quot;&gt;None&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;s&quot;&gt;&quot;expires_in&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;-&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;100&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;},&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

    &lt;p&gt;This session object can be used the same way as the main Requests API:&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-python&quot; data-lang=&quot;python&quot;&gt;&lt;span class=&quot;n&quot;&gt;session&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;.&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;get&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;https://example.com/Users&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

    &lt;p&gt;The difference is, the session will automatically fetch the access token and attach it to every subsequent request.&lt;/p&gt;
    &lt;p&gt;No need to add an Authorization header to every single API call anymore.&lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">Lately I've been writing a lot of background jobs that need to interact with different OAuth 2 service providers. Not knowing any better, I coded my own authorization logic using the Requests library. This approach works, but there's a better solution.</summary></entry><entry><title type="html">PHP quiz #3 - operator associativity</title><link href="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-3-associativity.html" rel="alternate" type="text/html" title="PHP quiz #3 - operator associativity" /><published>2019-06-16T00:00:00+01:00</published><updated>2019-06-16T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2019/06/16/php-quiz-part-3-associativity</id><content type="html" xml:base="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-3-associativity.html">&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Question&lt;/h2&gt;
  &lt;p&gt;What will this code output?&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;nv&quot;&gt;$x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;nv&quot;&gt;$y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;4&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;nv&quot;&gt;$z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;6&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;gt;&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;gt;&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'true'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;else&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'false'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;ul class=&quot;answers&quot;&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;A&lt;/span&gt;
      &lt;pre&gt;Syntax error&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;pre&gt;true&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;pre&gt;false&lt;/pre&gt;
    &lt;/li&gt;
  &lt;/ul&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Answer&lt;/h2&gt;
  &lt;a id=&quot;show-answer&quot; href=&quot;#&quot;&gt;Show the answer&lt;/a&gt;
  &lt;div id=&quot;answer&quot;&gt;
    &lt;div class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;A&lt;/span&gt;
      &lt;pre&gt;Syntax error&lt;/pre&gt;
    &lt;/div&gt;
  &lt;/div&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Explanation&lt;/h2&gt;
  &lt;h3&gt;Operator associativity&lt;/h3&gt;
  &lt;p&gt;Operator associativity decides how operators of equal precedence are grouped.&lt;/p&gt;
  &lt;table&gt;
    &lt;thead&gt;
      &lt;tr&gt;
        &lt;th&gt;operator&lt;/th&gt;
        &lt;th&gt;associativity&lt;/th&gt;
        &lt;th&gt;example&lt;/th&gt;
        &lt;th&gt;result&lt;/th&gt;
      &lt;/tr&gt;
    &lt;/thead&gt;
    &lt;tbody&gt;
      &lt;tr&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;+&lt;/code&gt; (addition)&lt;/td&gt;
        &lt;td&gt;left&lt;/td&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;1 + 2 + 3&lt;/code&gt;&lt;/td&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;(1 + 2) + 3&lt;/code&gt;&lt;/td&gt;
      &lt;/tr&gt;
      &lt;tr&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;=&lt;/code&gt; (assignment)&lt;/td&gt;
        &lt;td&gt;right&lt;/td&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;$a = $b = $c&lt;/code&gt;&lt;/td&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;$a = ($b = $c)&lt;/code&gt;&lt;/td&gt;
      &lt;/tr&gt;
    &lt;/tbody&gt;
  &lt;/table&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Non-associative operators&lt;/h3&gt;
  &lt;p&gt;
    In PHP, however, comparison operators are &lt;em&gt;non-associative&lt;/em&gt;.
    They cannot be used next to each other.
  &lt;/p&gt;
  &lt;p&gt;The expression &lt;code class=&quot;highlighter-rouge&quot;&gt;$z &gt; $y &gt; $x&lt;/code&gt; is illegal.&lt;/p&gt;
  &lt;table&gt;
    &lt;thead&gt;
      &lt;tr&gt;
        &lt;th&gt;operator&lt;/th&gt;
        &lt;th&gt;associativity&lt;/th&gt;
        &lt;th&gt;example&lt;/th&gt;
        &lt;th&gt;result&lt;/th&gt;
      &lt;/tr&gt;
    &lt;/thead&gt;
    &lt;tbody&gt;
      &lt;tr&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;&amp;gt;&lt;/code&gt; (greater-than)&lt;/td&gt;
        &lt;td&gt;non-associative&lt;/td&gt;
        &lt;td&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;$z &amp;gt; $y &amp;gt; $x&lt;/code&gt;&lt;/td&gt;
        &lt;td&gt;syntax error&lt;/td&gt;
      &lt;/tr&gt;
    &lt;/tbody&gt;
  &lt;/table&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Other languages&lt;/h3&gt;
  &lt;p&gt;
    Most programming languages do not allow the &lt;a href=&quot;https://en.wikipedia.org/wiki/Relational_operator#Operator_chaining&quot;&gt;chaining of relational operators&lt;/a&gt;.
    The desired result is usually achieved with something like &lt;code class=&quot;highlighter-rouge&quot;&gt;$z &gt; $y &amp;&amp; $y &gt; $x&lt;/code&gt;.
  &lt;/p&gt;
  &lt;p&gt;
    A notable exception is Python.
    It evaluates chained relational operators the way someone less scarred by programming would expect:
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-python&quot; data-lang=&quot;python&quot;&gt;&lt;span class=&quot;n&quot;&gt;x&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;
&lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;4&lt;/span&gt;
&lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;6&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;z&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;gt;&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;y&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;gt;&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;x&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;'true'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;else&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;:&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;print&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;'false'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;# true&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;Awesome!&lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Credits&lt;/h3&gt;
  &lt;p&gt;This post was inspired by Upwork's ridiculously incorrect &lt;a href=&quot;https://www.upwork.com/i/interview-questions/php/&quot;&gt;PHP interview question&lt;/a&gt;.&lt;/p&gt;
  &lt;p style=&quot;text-align: center&quot;&gt;
    &lt;img src=&quot;/assets/images/php-quiz-part-3/upwork-question.png&quot; alt=&quot;Upwork question&quot; title=&quot;Upwork question&quot; /&gt;
  &lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">Operators are the building blocks of computer programs. You might think you know them, but the devil is in the details. After all these years, I still find myself revisiting the precedence table every once in a while.</summary></entry><entry><title type="html">PHP quiz #4 - hoisting</title><link href="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-4-hoisting.html" rel="alternate" type="text/html" title="PHP quiz #4 - hoisting" /><published>2019-06-16T00:00:00+01:00</published><updated>2019-06-16T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2019/06/16/php-quiz-part-4-hoisting</id><content type="html" xml:base="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-4-hoisting.html">&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Question&lt;/h2&gt;
  &lt;p&gt;What will this code output?&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;helloWorld&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;();&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;helloWorld&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;Hello World!&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;ul class=&quot;answers&quot;&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;A&lt;/span&gt;
      &lt;span&gt;Fatal error: Uncaught Error: Call to undefined function helloWorld()&lt;/span&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;span&gt;Nothing&lt;/span&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;span&gt;Hello World!&lt;/span&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;D&lt;/span&gt;
      &lt;span&gt;Warning + &quot;helloWorld()&quot;&lt;/span&gt;
    &lt;/li&gt;
  &lt;/ul&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Answer&lt;/h2&gt;
  &lt;a id=&quot;show-answer&quot; href=&quot;#&quot;&gt;Show the answer&lt;/a&gt;
  &lt;div id=&quot;answer&quot;&gt;
    &lt;div class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;pre&gt;Hello World!&lt;/pre&gt;
    &lt;/div&gt;
  &lt;/div&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Explanation&lt;/h2&gt;
  &lt;h3&gt;Hoisting&lt;/h3&gt;
  &lt;p&gt;
    Similarly to JavaScript, function declarations are resolved at compile time.
    By the time the interpreter calls our function, it will have been already defined.
    The program will run without any problems.
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Restrictions on hoisting&lt;/h3&gt;
  &lt;p&gt;
    When the function is defined conditionally, this is not the case.
    For hoisting to work, it has to be defined on the top level.
    The following will throw a fatal error:
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;if&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kc&quot;&gt;true&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;c1&quot;&gt;// Fatal error: Uncaught Error: Call to undefined function helloWorld().&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;helloWorld&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;();&lt;/span&gt;

  &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;helloWorld&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;Hello World!&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Includes&lt;/h3&gt;
  &lt;p&gt;What about includes?&lt;/p&gt;
  &lt;p&gt;
    Naturally, they are only resolved at runtime.
    When including a function, the include statement must run before the function call.
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// Fatal error: Uncaught Error: Call to undefined function helloWorld().&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;helloWorld&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;();&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// Includes the helloWorld function.&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;include&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;helloWorld.php&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Classes&lt;/h3&gt;
  &lt;p&gt;Functions are not the only unit of code organization (thank God!).&lt;/p&gt;
  &lt;p&gt;
    Hoisting applies to class, interface and trait declarations too.
    More or less.
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// OK!&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;p&gt;It becomes less graceful when multiple levels of inheritance is introduced.&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;C&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;C&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// Fatal error: Class 'B' not found in ...&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;p&gt;It's not that big of a problem though.&lt;/p&gt;
  &lt;p&gt;
    Avoiding top level functions and declaring one class per file is considered as best practice.
    This eliminates the possibility of ever relying on PHP to hoist your code.
  &lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">The term &quot;hoisting&quot; is used exclusively by JavaScript to describe its feature of moving variable and function declarations to the top of the current scope. Other languages have concepts resembling hoisting too, but for some reason they aren't discussed nearly as much as they should be.</summary></entry><entry><title type="html">PHP quiz #5 - constructor overriding</title><link href="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-5-constructors.html" rel="alternate" type="text/html" title="PHP quiz #5 - constructor overriding" /><published>2019-06-16T00:00:00+01:00</published><updated>2019-06-16T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2019/06/16/php-quiz-part-5-constructors</id><content type="html" xml:base="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-5-constructors.html">&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Question&lt;/h2&gt;
  &lt;p&gt;What will this code output?&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;__construct&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;LogicException&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$l&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;A&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;__construct&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;Exception&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$e&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;B&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;new&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;B&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;new&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;Exception&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s1&quot;&gt;'Exception!'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;));&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;ul class=&quot;answers&quot;&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;A&lt;/span&gt;
      &lt;span&gt;Warning: Declaration of B::__construct(Exception $e) should be compatible with A::__construct(LogicException $l)&lt;/span&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;pre&gt;B&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;pre&gt;AB&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;span&gt;Fatal error: Uncaught Exception: Exception!&lt;/span&gt;
    &lt;/li&gt;
  &lt;/ul&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Answer&lt;/h2&gt;
  &lt;a id=&quot;show-answer&quot; href=&quot;#&quot;&gt;Show the answer&lt;/a&gt;
  &lt;div id=&quot;answer&quot;&gt;
    &lt;div class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;pre&gt;B&lt;/pre&gt;
    &lt;/div&gt;
  &lt;/div&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Explanation&lt;/h2&gt;
  &lt;p&gt;In PHP, the only rule to overriding constructors is that &lt;strong&gt;there are no rules&lt;/strong&gt;!&lt;/p&gt;
  &lt;p&gt;
    Constructors can be overridden with &lt;em&gt;any&lt;/em&gt; signature.
    Their parameters can be changed freely and without consequence.
  &lt;/p&gt;
  &lt;p&gt;They can be overridden with completely unrelated parameter types:&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;__construct&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;array&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;c1&quot;&gt;// Works fine!&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;__construct&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;Closure&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$c&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;Parameters can also be omitted (or added):&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;__construct&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;array&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;c1&quot;&gt;// This is OK too.&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;__construct&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Overriding functions&lt;/h3&gt;
  &lt;p&gt;
    Note that this kind of freedom only applies to constructors.
    Were these functions not constructors, PHP would issue a warning:
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;abc&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;LogicException&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$l&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;B&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;c1&quot;&gt;// Warning: Declaration of B::abc(Exception $e) should be&lt;/span&gt;
  &lt;span class=&quot;c1&quot;&gt;// compatible with A::abc(LogicException $l)&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;abc&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;Exception&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$e&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Credits&lt;/h3&gt;
  &lt;p&gt;This post was inspired by an inaccurate &lt;a href=&quot;https://en.wikipedia.org/wiki/Talk:Covariance_and_contravariance_(computer_science)#Inaccurate_PHP_example&quot;&gt;Wikipedia article&lt;/a&gt;.&lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">Most PHP developers probably have already used constructor overriding, as it would be virtually impossible to create object oriented applications without it. Still, many of them might not be familiar with the exact rules around the subject - I know I wasn't.</summary></entry><entry><title type="html">PHP quiz #6 - covariance</title><link href="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-6-covariance.html" rel="alternate" type="text/html" title="PHP quiz #6 - covariance" /><published>2019-06-16T00:00:00+01:00</published><updated>2019-06-16T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2019/06/16/php-quiz-part-6-covariance</id><content type="html" xml:base="https://csirmazbendeguz.net/2019/06/16/php-quiz-part-6-covariance.html">&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Question&lt;/h2&gt;
  &lt;p&gt;Will this code throw a warning (PHP 7.1)?&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;array&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassB&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;iterable&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;ul class=&quot;answers&quot;&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;A&lt;/span&gt;
      &lt;span&gt;Yes&lt;/span&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;pre&gt;No&lt;/pre&gt;
    &lt;/li&gt;
  &lt;/ul&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Answer&lt;/h2&gt;
  &lt;a id=&quot;show-answer&quot; href=&quot;#&quot;&gt;Show the answer&lt;/a&gt;
  &lt;div id=&quot;answer&quot;&gt;
    &lt;div class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;span&gt;No&lt;/span&gt;
    &lt;/div&gt;
    &lt;p&gt;There are a few cases where functions can be overridden with certain signatures.&lt;/p&gt;
  &lt;/div&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Iterable&lt;/h2&gt;
  &lt;p&gt;&lt;code class=&quot;highlighter-rouge&quot;&gt;iterable&lt;/code&gt; is a pseudo-type introduced in PHP 7.1.&lt;/p&gt;
  &lt;p style=&quot;text-align:center;&quot;&gt;
    &lt;img src=&quot;/assets/images/php-quiz-part-6-covariance/iterable.png&quot; alt=&quot;iterable's inheritance tree&quot; title=&quot;iterable's inheritance tree&quot; /&gt;
  &lt;/p&gt;
  &lt;p&gt;It's like an abstract base class for variables that can be &lt;em&gt;iterated&lt;/em&gt; with foreach (arrays, Traversable objects).&lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Variance (recap)&lt;/h2&gt;
  &lt;p&gt;When a subclass overrides a method of a superclass, it is possible to change its parameter and return types.&lt;/p&gt;
  &lt;table style=&quot;margin: 0 auto;&quot;&gt;
    &lt;thead&gt;
      &lt;tr&gt;
        &lt;th&gt;Covariance&lt;/th&gt;
        &lt;th&gt;Contravariance&lt;/th&gt;
        &lt;th&gt;Invariance&lt;/th&gt;
      &lt;/tr&gt;
    &lt;/thead&gt;
    &lt;tbody&gt;
      &lt;tr&gt;
        &lt;td&gt;&lt;img src=&quot;/assets/images/php-quiz-part-6-covariance/covariance.svg&quot; alt=&quot;Covariance&quot; title=&quot;Covariance&quot; /&gt;&lt;/td&gt;
        &lt;td&gt;&lt;img src=&quot;/assets/images/php-quiz-part-6-covariance/contravariance.svg&quot; alt=&quot;Contravariance&quot; title=&quot;Contravariance&quot; /&gt;&lt;/td&gt;
        &lt;td&gt;&lt;img src=&quot;/assets/images/php-quiz-part-6-covariance/invariance.svg&quot; alt=&quot;Invariance&quot; title=&quot;Invariance&quot; /&gt;&lt;/td&gt;
      &lt;/tr&gt;
    &lt;/tbody&gt;
  &lt;/table&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Covariance&lt;/h3&gt;
  &lt;p&gt;
    Covariance means overriding methods can return &lt;em&gt;more&lt;/em&gt; specific types.
    An &lt;code class=&quot;highlighter-rouge&quot;&gt;array&lt;/code&gt; is more specific than an &lt;code class=&quot;highlighter-rouge&quot;&gt;iterable&lt;/code&gt;.
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;iterable&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;[];&lt;/span&gt;
  &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassB&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;array&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;[];&lt;/span&gt;
  &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;p&gt;
    Note that this is type safe.
    I like to think about the following pseudocode to justify why it works:
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-text&quot; data-lang=&quot;text&quot;&gt;ClassA obj = new ClassB();
iterable retval = obj.method();&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;p&gt;
    Polymorphism allows us to use a subclass's (ClassB) instance anywhere where a superclass's (ClassA) instance is expected.
    When a subclass overrides a method, it must respect the type constraints set by its parent.
  &lt;/p&gt;
  &lt;p&gt;
    In other words, the overriding method must return an iterable.
    Since an array is an iterable, this requirement is satisfied.
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Contravariance&lt;/h3&gt;
  &lt;p&gt;
    Contravariance means overriding methods can accept &lt;em&gt;less&lt;/em&gt; specific parameters.
    An &lt;code class=&quot;highlighter-rouge&quot;&gt;iterable&lt;/code&gt; is less specific than an &lt;code class=&quot;highlighter-rouge&quot;&gt;array&lt;/code&gt;.
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;array&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassB&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;iterable&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;p&gt;
    This is type safe too.
    It's a bit harder to reason about, but here's my try:
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-text&quot; data-lang=&quot;text&quot;&gt;ClassA obj = new ClassB();
obj.method(new array());&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;p&gt;
    Polymorphism allows us to use a subclass's (ClassB) instance anywhere where a superclass's (ClassA) instance is expected.
    When a subclass overrides a method, it must respect the type constraints set by its parent.
  &lt;/p&gt;
  &lt;p&gt;
    In this case, the overriding method must be able to receive an array type parameter.
    Accepting all iterables (including arrays) satisfies this requirement.
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Invariance&lt;/h3&gt;
  &lt;p&gt;Invariance means the overriding method cannot change the types.&lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Covariance, contravariance and PHP&lt;/h2&gt;
  &lt;p&gt;
    PHP does &lt;em&gt;not&lt;/em&gt; support covariance/contravariance.
    It's an invariant language.
    However, as always, there are a few exceptions:
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;1. iterable&lt;/h3&gt;
  &lt;p&gt;By now it shouldn't come as a surprise that &lt;code class=&quot;highlighter-rouge&quot;&gt;iterable&lt;/code&gt; is indeed covariant/contravariant.&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;k&quot;&gt;array&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;iterable&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;[];&lt;/span&gt;
  &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassB&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;iterable&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;array&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
    &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;[];&lt;/span&gt;
  &lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;2. parameter type widening&lt;/h3&gt;
  &lt;p&gt;
    From PHP 7.2 you can omit parameter types in overriding methods.
    This is an example of contravariance.
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nx&quot;&gt;Exception&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$e&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassB&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$e&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;3. return types&lt;/h3&gt;
  &lt;p&gt;
    If the parent method doesn’t have a return type, it can be specified.
    This is an example of covariance.
  &lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;ClassB&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;extends&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;ClassA&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;method&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;:&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;void&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{}&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;The future&lt;/h2&gt;
  &lt;p&gt;
    PHP is mostly invariant, for now.
    But there is progress!
  &lt;/p&gt;
  &lt;p&gt;
    PHP 7.4 is going to add support for real covariance/contravariance (&lt;a href=&quot;https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters&quot;&gt;rfc&lt;/a&gt;).
    It will be a great improvement to PHP's type system.
  &lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">A complete guide to covariance and contravariance in PHP 7.1.</summary></entry><entry><title type="html">PHP quiz #2 - echo</title><link href="https://csirmazbendeguz.net/2019/06/15/php-quiz-part-2-echoes.html" rel="alternate" type="text/html" title="PHP quiz #2 - echo" /><published>2019-06-15T00:00:00+01:00</published><updated>2019-06-15T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2019/06/15/php-quiz-part-2-echoes</id><content type="html" xml:base="https://csirmazbendeguz.net/2019/06/15/php-quiz-part-2-echoes.html">&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Question&lt;/h2&gt;
  &lt;p&gt;What will this code output?&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'a'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;return&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'a'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'b'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(),&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;c&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;ul class=&quot;answers&quot;&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;A&lt;/span&gt;
      &lt;pre&gt;bac
a&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;pre&gt;baac&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;pre&gt;abac&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;D&lt;/span&gt;
      &lt;pre&gt;abc
a&lt;/pre&gt;
    &lt;/li&gt;
  &lt;/ul&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Answer&lt;/h2&gt;
  &lt;a id=&quot;show-answer&quot; href=&quot;#&quot;&gt;Show the answer&lt;/a&gt;
  &lt;div id=&quot;answer&quot;&gt;
    &lt;div class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;pre&gt;baac&lt;/pre&gt;
    &lt;/div&gt;
  &lt;/div&gt;
&lt;/section&gt;


&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Explanation&lt;/h2&gt;
  &lt;p&gt;
    If you're like me, you've probably guessed &quot;abac&quot;, and under any other
    circumstances you would have been right.
  &lt;/p&gt;
  &lt;p&gt;When calling a function, every argument is evaluated before entering the function body.&lt;/p&gt;
  &lt;p style=&quot;text-align:center;&quot;&gt;
    &lt;img src=&quot;/assets/images/php-quiz-part-2/parameters-vs-arguments.png&quot; alt=&quot;Parameters vs Arguments&quot; title=&quot;Parameters vs Arguments&quot;/&gt;
  &lt;/p&gt;
  &lt;p&gt;
    The catch is, &lt;strong&gt;echo is not a function&lt;/strong&gt;.
    It's a language construct.
    It has special meaning for the interpreter, and as such, it works a little differently.
  &lt;/p&gt;
  &lt;p&gt;Instead of evaluating all the arguments eagerly, it evaluates them &lt;em&gt;one by one&lt;/em&gt;.&lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Variable declarations&lt;/h3&gt;
  &lt;p&gt;
    To understand the rationale behind echo's strange behaviour, consider variable declarations.
  &lt;/p&gt;
  &lt;p&gt;
    PHP allows declaring multiple variables in a single statement.
    The two code snippets below have the exact same effect:
  &lt;/p&gt;
  &lt;div class=&quot;compare-table&quot;&gt;
    &lt;table&gt;
      &lt;tbody&gt;
        &lt;tr&gt;
          &lt;td&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'a'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;global&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$c&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$d&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;static&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$e&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'e'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
          &lt;/td&gt;
          &lt;td&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;class&lt;/span&gt; &lt;span class=&quot;nc&quot;&gt;A&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'a'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;public&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;nf&quot;&gt;b&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;()&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;global&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$c&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;global&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$d&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;static&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$e&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'e'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;static&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$f&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
          &lt;/td&gt;
        &lt;/tr&gt;
      &lt;/tbody&gt;
    &lt;/table&gt;
  &lt;/div&gt;
  &lt;p&gt;
    Although echo doesn't have much in common with variable declarations conceptually,
    it handles multiple arguments in a very similar way:
  &lt;/p&gt;
  &lt;div class=&quot;compare-table&quot;&gt;
    &lt;table&gt;
      &lt;tbody&gt;
      &lt;tr&gt;
        &lt;td&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'b'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(),&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;c&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
        &lt;/td&gt;
        &lt;td&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s1&quot;&gt;'b'&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;nx&quot;&gt;a&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;();&lt;/span&gt;
&lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;c&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
        &lt;/td&gt;
      &lt;/tr&gt;
      &lt;/tbody&gt;
    &lt;/table&gt;
  &lt;/div&gt;
  &lt;p&gt;
    That is, passing multiple arguments to echo is essentially the same as writing
    separate, consecutive echo statements.
  &lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">When people get into PHP development, the first thing they usually learn is the echo statement. Despite its elementary nature, I've found its handling of multiple arguments to be quite tricky.</summary></entry><entry><title type="html">PHP quiz #1 - for loop</title><link href="https://csirmazbendeguz.net/2019/06/14/php-quiz-part-1-for-loops.html" rel="alternate" type="text/html" title="PHP quiz #1 - for loop" /><published>2019-06-14T00:00:00+01:00</published><updated>2019-06-14T00:00:00+01:00</updated><id>https://csirmazbendeguz.net/2019/06/14/php-quiz-part-1-for-loops</id><content type="html" xml:base="https://csirmazbendeguz.net/2019/06/14/php-quiz-part-1-for-loops.html">&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Question&lt;/h2&gt;
  &lt;p&gt;What will this code output?&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;cp&quot;&gt;&amp;lt;?php&lt;/span&gt;

&lt;span class=&quot;k&quot;&gt;for&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;++&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;++&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;{&lt;/span&gt;
  &lt;span class=&quot;k&quot;&gt;echo&lt;/span&gt; &lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;,&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s2&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;
&lt;span class=&quot;p&quot;&gt;}&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;ul class=&quot;answers&quot;&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;A&lt;/span&gt;
      &lt;pre&gt;Syntax error&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;B&lt;/span&gt;
      &lt;pre&gt;0,0
1,1
2,2&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;pre&gt;0,0
1,1&lt;/pre&gt;
    &lt;/li&gt;
    &lt;li class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;D&lt;/span&gt;
      &lt;pre&gt;0,0
1,1
2,1&lt;/pre&gt;
    &lt;/li&gt;
  &lt;/ul&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Answer&lt;/h2&gt;
  &lt;a id=&quot;show-answer&quot; href=&quot;#&quot;&gt;Show the answer&lt;/a&gt;
  &lt;div id=&quot;answer&quot;&gt;
    &lt;div class=&quot;answer&quot;&gt;
      &lt;span class=&quot;answer-letter&quot;&gt;C&lt;/span&gt;
      &lt;pre&gt;0,0
1,1&lt;/pre&gt;
    &lt;/div&gt;
  &lt;/div&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h2&gt;Explanation&lt;/h2&gt;
  &lt;h3&gt;The for loop header&lt;/h3&gt;
  &lt;p&gt;
    Similarly to other languages, it is perfectly legal to initialize and update multiple variables in for loop headers.
    Consider the following:
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;k&quot;&gt;for&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;0&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;...&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;++&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;++&lt;/span&gt;&lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;c1&quot;&gt;// OK!&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;
    This is a valid PHP code snippet, and it does exactly what you would expect:
    it introduces two variables, &lt;code class=&quot;highlighter-rouge&quot;&gt;$i&lt;/code&gt; and &lt;code class=&quot;highlighter-rouge&quot;&gt;$j&lt;/code&gt;,
    with the initial value of &lt;code class=&quot;highlighter-rouge&quot;&gt;0&lt;/code&gt;,
    and it increments them by one at the end of each iteration.
  &lt;/p&gt;
  &lt;p&gt;No trickery here.&lt;/p&gt;
  &lt;p&gt;The difficulty lies in the loop's condition:&lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;k&quot;&gt;for&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;...&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;...&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt; &lt;span class=&quot;c1&quot;&gt;// ???&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;
    It might not be immediately obvious what effect does this code have on the loop.
    One thing's for sure: it won't throw any syntax errors, it's syntactically correct.
  &lt;/p&gt;
  &lt;aside class=&quot;comment&quot;&gt;
    &lt;p&gt;
      At first glance, it might seem like the loop defines multiple conditions that are eventually &lt;em&gt;AND&lt;/em&gt;ed together.
      This is a fair guess and it's not without reason.
      Haskell does something similar - it &lt;em&gt;AND&lt;/em&gt;s together multiple predicates in list comprehensions.
    &lt;/p&gt;
    &lt;p&gt;This is not the case here.&lt;/p&gt;
    &lt;p&gt;
      PHP has its roots in C.
      As such, it has a few weird historical remains that at first may sound completely counterintuitive.
    &lt;/p&gt;
  &lt;/aside&gt;
  &lt;p&gt;
    Surprising as it may seem, &lt;code class=&quot;highlighter-rouge&quot;&gt;$i &lt; 3, $j &lt; 2&lt;/code&gt; is actually a
    &lt;strong&gt;single expression&lt;/strong&gt;, and as all expressions, it evaluates to something.
  &lt;/p&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Comma operator (C)&lt;/h3&gt;
  &lt;p&gt;In C, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Comma_operator&quot;&gt;comma operator&lt;/a&gt; (&lt;code class=&quot;highlighter-rouge&quot;&gt;,&lt;/code&gt;) is an operator that evaluates two expressions and returns the result of the second one.&lt;/p&gt;
  &lt;p&gt;
    For example, the following code prints the text &lt;code class=&quot;highlighter-rouge&quot;&gt;Hello World!&lt;/code&gt; to stdout,
    and assigns &lt;code class=&quot;highlighter-rouge&quot;&gt;3&lt;/code&gt; to variable &lt;code class=&quot;highlighter-rouge&quot;&gt;a&lt;/code&gt;:
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-c&quot; data-lang=&quot;c&quot;&gt;&lt;span class=&quot;kt&quot;&gt;int&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;printf&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;Hello World!&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;),&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;+&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;);&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

  &lt;p&gt;The paranthesized expression is evaluated something like this:&lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-c&quot; data-lang=&quot;c&quot;&gt;&lt;span class=&quot;cm&quot;&gt;/* 0. */&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;printf&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;Hello World!&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;),&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;+&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;
&lt;span class=&quot;cm&quot;&gt;/* 1. */&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;13&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;
&lt;span class=&quot;cm&quot;&gt;/* 2. */&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;aside class=&quot;comment&quot;&gt;
    &lt;code class=&quot;highlighter-rouge&quot;&gt;printf&lt;/code&gt; returns the number of characters
    printed (&lt;code class=&quot;highlighter-rouge&quot;&gt;13&lt;/code&gt; in our case).
  &lt;/aside&gt;
  &lt;aside class=&quot;comment&quot;&gt;
    &lt;p&gt;
      Notice the parentheses around the expression in question.
      They are there for a reason.
    &lt;/p&gt;
    &lt;p&gt;
      In C, the comma operator has the lowest precedence of all operators.
      Its precedence is even lower than the assignment operator's (&lt;code class=&quot;highlighter-rouge&quot;&gt;=&lt;/code&gt;)!
    &lt;/p&gt;
    &lt;p&gt;That is to say, omitting the parentheses would result in the code being parsed like this:&lt;/p&gt;

&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-c&quot; data-lang=&quot;c&quot;&gt;&lt;span class=&quot;kt&quot;&gt;int&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;printf&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;Hello World!&lt;/span&gt;&lt;span class=&quot;se&quot;&gt;\n&lt;/span&gt;&lt;span class=&quot;s&quot;&gt;&quot;&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)),&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;+&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;

    &lt;p&gt;Which, of course, wouldn't make any sense.&lt;/p&gt;
  &lt;/aside&gt;
&lt;/section&gt;

&lt;section class=&quot;section&quot;&gt;
  &lt;h3&gt;Comma operator (PHP)&lt;/h3&gt;
  &lt;p&gt;
    This ancient operator did not stand the test of time,
    not many programming languages support it.
  &lt;/p&gt;
  &lt;p&gt;
    PHP doesn't do either.
    It's not listed in the &lt;a href=&quot;https://www.php.net/manual/en/language.operators.precedence.php&quot;&gt;precedence table&lt;/a&gt; and using it will generally result in a syntax error.
  &lt;/p&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-c&quot; data-lang=&quot;c&quot;&gt;&lt;span class=&quot;o&quot;&gt;&amp;lt;?&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;php&lt;/span&gt;

&lt;span class=&quot;c1&quot;&gt;// Parse error: syntax error, unexpected ',' in ...&lt;/span&gt;
&lt;span class=&quot;err&quot;&gt;$&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;a&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;=&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;mi&quot;&gt;1&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;);&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
  &lt;p&gt;However, surprisingly, there is an exception to the rule: for loop conditions.&lt;/p&gt;
  &lt;p&gt;For some strange reason, in for loop conditions the comma operator is correctly evaluated.&lt;/p&gt;
  &lt;div class=&quot;compare-table&quot;&gt;
    &lt;table&gt;
      &lt;tbody&gt;
      &lt;tr&gt;
        &lt;td&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;k&quot;&gt;for&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;...&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$i&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;3&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;,&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;...&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
        &lt;/td&gt;
        &lt;td&gt;
&lt;figure class=&quot;highlight&quot;&gt;&lt;pre&gt;&lt;code class=&quot;language-php&quot; data-lang=&quot;php&quot;&gt;&lt;span class=&quot;k&quot;&gt;for&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;o&quot;&gt;...&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;nv&quot;&gt;$j&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;&amp;lt;&lt;/span&gt; &lt;span class=&quot;mi&quot;&gt;2&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;;&lt;/span&gt; &lt;span class=&quot;o&quot;&gt;...&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;)&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;&lt;/figure&gt;
        &lt;/td&gt;
      &lt;/tr&gt;
      &lt;/tbody&gt;
    &lt;/table&gt;
  &lt;/div&gt;
  &lt;p&gt;
    In this case, the expression &lt;code class=&quot;highlighter-rouge&quot;&gt;$i &lt; 3, $j &lt; 2&lt;/code&gt; has the same effect as &lt;code class=&quot;highlighter-rouge&quot;&gt;$j &lt; 2&lt;/code&gt;.
    The first operand is evaluated, but its result is discarded.
  &lt;/p&gt;
  &lt;p&gt;The loop will only iterate twice.&lt;/p&gt;
&lt;/section&gt;</content><author><name></name></author><summary type="html">For loops are one of the most fundamental and ubiquitous control flow statements. They are so essential to computer programming, you would expect every developer to know them inside out. As for me, I never would have thought I could learn anything new about them - I was wrong.</summary></entry></feed>