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To: Larry Garfield <larry@garfieldtech.com>, internals@lists.php.net
Cc: php internals <internals@lists.php.net>, Marco Pivetta <ocramius@gmail.com>
Date: Thu, 09 Jun 2022 20:15:20 +0200
Message-ID: <21891029.EfDdHjke4D@arnaud-t490>
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Subject: Re: [PHP-DEV] [RFC] Short Closures 2, aka auto-capture take 3
From: arnaud.lb@gmail.com (Arnaud Le Blanc)

Hi,

On jeudi 9 juin 2022 18:46:53 CEST Marco Pivetta wrote: 
> ## nesting these functions within each other
> 
> What happens when/if we nest these functions? Take this minimal example:
> 
> ```php
> $a = 'hello world';
> 
> (fn () {
>     (fn () {
>         echo $a;
>     })();
> })();
> ```

Capture bubbles up. When an inner function uses a variable, the outer function 
in fact uses it too, so it's captured by both functions, by-value.

This example prints "hello world": The inner function captures $a from the 
outer function, which captures $a from its declaring scope.

This is equivalent to

```php
(function () use ($a) {
    (function () use ($a) {
        echo $a;
    })();
})();
```

> ## capturing `$this`
> 
> In the past (also present), I had to type `static fn () => ...` or `static
> function () { ...` all over the place, to avoid implicitly binding `$this`
> to a closure, causing hidden memory leaks.
> 
> Assuming following:
> 
>  * these new closures could capture `$this` automatically, once detected
>  * these new closures can optimize away unnecessary variables that aren't
> captured
> 
> Would that allow us to get rid of `static fn () {` declarations, when
> creating one of these closures in an instance method context?

It would be great to get rid of this, but ideally this would apply to Arrow 
Functions and Anonymous Functions as well. This could be a separate RFC.

--
Arnaud Le Blanc