defer #403
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odino
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May 13, 2021
Sometimes it is very helpful to guarantee a certain function is executed
regardless of what code path we take: you can use the `defer` keyword for
this.
```py
echo(1)
defer echo(3)
echo(2)
```
When you schedule a function to be deferred, it will executed right at
the end of the current scope. A `defer` inside a function will then
execute at the end of that function itself:
```py
echo(1)
f fn() {
defer echo(3)
echo(2)
}
fn()
echo(4)
```
You can `defer` any callable: a function call, a method or even a system
command. This can be very helpful if you need to run a cleanup function
right before wrapping up with your code:
```sh
defer `rm my-file.txt`
"some text" > "my-file.txt"
...
...
"some other text" >> "my-file.txt"
```
In this case, you will be guaranteed to execute the command that removes
`my-file.txt` before the program closes.
Be aware that code that is deferred does not have access to the return value
of its scope, and will supress errors -- if a `defer` block messes up you're
not going to see any error. This behavior is experimental, but we would most
likely like to give this kind of control through [try...catch...finally](#118).
odino
added a commit
that referenced
this issue
May 24, 2021
Sometimes it is very helpful to guarantee a certain function is executed
regardless of what code path we take: you can use the `defer` keyword for
this.
```py
echo(1)
defer echo(3)
echo(2)
```
When you schedule a function to be deferred, it will executed right at
the end of the current scope. A `defer` inside a function will then
execute at the end of that function itself:
```py
echo(1)
f fn() {
defer echo(3)
echo(2)
}
fn()
echo(4)
```
You can `defer` any callable: a function call, a method or even a system
command. This can be very helpful if you need to run a cleanup function
right before wrapping up with your code:
```sh
defer `rm my-file.txt`
"some text" > "my-file.txt"
...
...
"some other text" >> "my-file.txt"
```
In this case, you will be guaranteed to execute the command that removes
`my-file.txt` before the program closes.
Be aware that code that is deferred does not have access to the return value
of its scope, and will supress errors -- if a `defer` block messes up you're
not going to see any error. This behavior is experimental, but we would most
likely like to give this kind of control through [try...catch...finally](#118).
odino
added a commit
that referenced
this issue
Apr 14, 2022
Sometimes it is very helpful to guarantee a certain function is executed
regardless of what code path we take: you can use the `defer` keyword for
this.
```py
echo(1)
defer echo(3)
echo(2)
```
When you schedule a function to be deferred, it will executed right at
the end of the current scope. A `defer` inside a function will then
execute at the end of that function itself:
```py
echo(1)
f fn() {
defer echo(3)
echo(2)
}
fn()
echo(4)
```
You can `defer` any callable: a function call, a method or even a system
command. This can be very helpful if you need to run a cleanup function
right before wrapping up with your code:
```sh
defer `rm my-file.txt`
"some text" > "my-file.txt"
...
...
"some other text" >> "my-file.txt"
```
In this case, you will be guaranteed to execute the command that removes
`my-file.txt` before the program closes.
Be aware that code that is deferred does not have access to the return value
of its scope, and will supress errors -- if a `defer` block messes up you're
not going to see any error. This behavior is experimental, but we would most
likely like to give this kind of control through [try...catch...finally](#118).
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