Defer experimental

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.

echo(1)
defer echo(3)
echo(2)
# 1
# 2
# 3

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:

echo(1)
f fn() {
    defer echo(3)
    echo(2)
}
fn()
echo(4)
# 1
# 2
# 3
# 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:

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 (opens new window).