Standard Library 0.99 chapter

NotTheDr01ds · NotTheDr01ds · commit 68cad3edc9f8 · 2024-10-11T08:56:55.000-04:00
diff --git a/book/standard_library.md b/book/standard_library.md
@@ -2,6 +2,10 @@
 
 Nushell ships with a standard library of useful commands written in native Nu. By default, the standard library is loaded into memory (but not automatically imported) when Nushell starts.
 
+[[toc]]
+
+## Overview
+
 The standard library currently includes:
 
 - Assertions
@@ -14,32 +18,218 @@ The standard library currently includes:
 To see a complete list of the commands available in the standard library, run the following:
 
 ```nu
-use std
-scope commands
-| where name =~ '^std '
-| select name usage extra_usage
-| wrap "std-lib"
+nu -c "
+  use std
+  scope commands
+  | where name =~ '^std '
+  | select name description extra_description
+  | wrap 'Standard Library Commands'
+  | table -e
+"
+```
+
+::: note
+The `use std` command above loads the entire standard library so that you can see all of the commands at once. This is typically not how it will be used (more info below). It is also run in a separate Nu subshell simply so that it is not loaded into scope in the shell you are using.
+:::
+
+## Importing the Standard Library
+
+While working at the commandline, it can be convenient to load the entire standard library using:
+
+```nu
+use std *
+```
+
+However, this form should be avoided in custom commands and scripts since it has the longest load time. While the load time is only on the order of ~20-30 milliseconds on an average system, that can add up in certain scenarios.
+
+::: important Optimal Startup when Using the Standard Library
+See the [notes below](#optimal-startup) on how to ensure that your configutation isn't loading the entire Standard Library.
+:::
+
+### Importing Submodules
+
+Each submodule of the standard library can be loaded separately. Again, for best performance, load only the submodule(s) that you need in your code.
+
+There are several forms that can be used:
+
+#### 1. Import the submodule
+
+Examples:
+
+```nu
+use std/iter
+[2 5 "4" 7] | iter filter-map {|it| $it ** 2}
+
+use std/help
+help ls
+help commands
+```
+
+This form requires that you prefix the command using the submodule name. This can be useful in two scenarios.
+
+1. In the `use std/iter` example, it's important to prefix the commands with the `iter` namespace. If, on the other hand, you were to `use std/iter *`, you would shadow the built-in `find` command with the `iter` module's `find` command.
+
+2. In the `use std/help` example, `help` is both the submodule name and the name of the main command it exports. Using `use std/help` allows you to access:
+
+   ```
+   help
+   help aliases
+   help modules
+   help commands
+   help operators
+   help externs
+   ```
+
+   In this case, the `std/help` commands are meant to shadow (replace) the built-in versions.
+
+Submodules that are normally imported with `use std/<submodule>`:
+
+- `use std/assert`: `assert` and its subcommands
+- `use std/bench`: The benchmarking command `bench`
+- `use std/dirs`: The directory stack command `dirs` and its subcommands
+- `use std/input`: The `input display` command
+- `use std/help`: An alternative version of the `help` command and its subcommands which supports completion and other features
+- `use std/iters`: Additional `iters`-prefixed iteration commands. Note: See-also alternative option #3 below.
+- `use std/log`: The `log <subcommands>` such as `log warning <msg>`
+- `use std/math`: Mathematical constants such as `$math.E`. These can also be imported without a prefix using Form #2 below.
+
+#### 2. Import all submodule commands without a prefix
+
+For certain submodules, you will want the commands from a submodule to be available in the current namespace, so that you _can_ simply access the command by name. For instance:
+
+```nu
+use std/formats *
+ls | to jsonl
+```
+
+Submodules that are normally imported with `use std/<submodule> *`:
+
+- `use std/dt *`: Additional commands for working with `date` values
+- `use std/formats *`: Additional `to` and `from` format conversions
+- `use std/math *`: The math constants without a prefix, such as `$E`. Note that the prefixed form #1 above is likely more understandable when reading and maintaining code.
+- `use std/xml *`: Additional commands for working with XML data
+
+#### 3. Importing specific subcommands
+
+As with most modules, you can choose to import only a subset of the commands. For instance, the following would import the `zip-with` command without requiring that it be called with`iter zip-with`.
+
+```nu
+use std/iter [ zip-with ]
+```
+
+#### 4. Not Recommended - `use std <submodule>` and `use std <submodule> *`
+
+While it is _possible_ to import Standard Library submodules using a space-separated form:
+
+```nu
+use std log
+use std formats *
+```
+
+This is NOT RECOMMENDED. Using this form has the same performance impact as:
+
+```nu
+use std *
+```
+
+::: caution
+The difference is subtle, but important from a performance perspective. Using `std/<submodules>` (with a slash) is far faster than `std <submodule>` (with a space):
+
+```nu
+bench -n 200 --pretty { nu -c "use std/formats *; exit" }
+# => 9ms 271µs 832ns +/- 328µs 860ns
+bench -n 200 --pretty { nu -c "use std formats *; exit" }
+# => 26ms 921µs 59ns +/- 588µs 919ns
 ```
 
-In addition, `stdlib-candidate`, found in the [nu_scripts Repository](https://github.com/nushell/nu_scripts/tree/main/stdlib-candidate/std-rfc), serves as a staging ground for new commands before they are added to the standard library.
+:::
+
+## The Standard Library Candidate Module
+
+(Also known as `std-rfc`)
+
+`stdlib-candidate`, found in the [nu_scripts Repository](https://github.com/nushell/nu_scripts/tree/main/stdlib-candidate/std-rfc), serves as a staging ground for new commands before they are added to the Standard Library.
+
+If you are interested in adding to the Standard Library, please submit your code via PR to the Candidate module in that repository. We also encourage you to install this module and provide feedback on upcoming candidate commands.
+
+::: details More details
+
+Candidate commands for the Standard Library should, in general:
+
+- Have broad appeal - Be useful to a large number of users or use cases
+- Be well-written and clearly commented for future maintainers
+- Implement help comments with example usage
+- Have a description that explains why you feel the command should be a part of the standard library. Think of this as an "advertisement" of sorts to convince people to try the command and provide feedback so that it can be promoted in the future.
+
+In order for a command to be graduated from RFC to the Standard Library, it must have:
+
+- Positive feedback
+- Few (or no) outstanding issues and, of course, no significant issues
+- A PR author for the `std` submission. This does not necessarily have to be the original author of the command.
+- Test cases as part of the `std` submission PR
+
+Ultimately a member of the core team will decide when and if to merge the command into `std` based on these criteria.
+
+Of course, if a candidate command in `std-rfc` no longer works or has too many issues, it may be removed from or disabled in `std-rfc`.
 
-::: tip Note
-Currently, parsing of the standard library impacts Nushell startup time. New commands are not being added to the library until this is resolved.
 :::
 
+## Disabling the Standard Library
+
 To disable the standard library, you can start using:
 
 ```nu
 nu --no-std-lib
 ```
 
-You will not be able to import the library using `use std *`, nor use any of its commands, if it is disabled in this way.
+This can be especially useful to minimize overhead when running a command in a subshell using `nu -c`. For example:
+
+```nu
+nu --no-std-lib -n -c "$nu.startup-time"
+# => 1ms 125µs 10ns
+
+nu -n -c "$nu.startup-time"
+# => 4ms 889µs 576ns
+```
+
+You will not be able to import the library, any of its submodules, nor use any of its commands, when it is disabled in this way.
+
+## Optimal Startup
+
+If Nushell's startup time is important to your workflow, review your [startup configuration]([./configuration.md]) in `config.nu`, `env.nu`, and potentially others for inefficient use of the standard library. The following command should identify any problem areas:
+
+```nu
+view files
+| enumerate | flatten
+| where filename !~ '^std'
+| where filename !~ '^entry'
+| where {|file|
+    (view span $file.start $file.end) =~ 'use\W+std[^\/]'
+  }
+```
+
+Edit those files to use the recommended syntax below.
+:::
+
+::: note
+If a Nushell library (e.g., from [the `nu_scripts` repository](https://github.com/nushell/nu_scripts)) is using this syntax, please report it via an issue or PR. These will be updated over time after Nushell 0.99.0 is released.
+
+If a third-party module is using this syntax, please report it to the author/maintainers to update.
+:::
+
+## Viewing Standard Library Source
 
 ::: tip Did You Know?
 Because the standard library is simply composed of [custom commands](./custom_commands.html) in [modules](./modules.html) and [submodules](./modules.html#submodules-and-subcommands), you can see the source for each command with the [`view source`](/commands/docs/view_source.md) command. For example, to view the source for the `ellie` command (with syntax highlighting):
 
 ```nu
-use std *
+use std/util *
 view source ellie | nu-highlight
 :::
+
+## Windows Path Syntax
+
+::: important
+Nushell on Windows supports both forward-slashes and back-slashes as the path separator.  However, to ensure cross-platform support for cripts and modules using `std`, using only the forward-slash `/` when importing Standard Library submodules is highly recommended.
+:::
 ```
