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Date: Thu, 20 Feb 2020 21:29:18 -0500
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To: Levi Morrison <levi.morrison@datadoghq.com>
Cc: Nikita Popov <nikita.ppv@gmail.com>, PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Explicit call-site pass-by-reference (again)
From: matthewmatthew@gmail.com (Matthew Brown)

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This proposal is great, but most PHP static analysis tools already do a
reasonable job of understanding by-reference assignment and detecting bugs
there (an exception is closure use by-reference checks, which is a
static-analysis no-man's land).

No static analysis tools catch your specific use-case, though.

On Thu, 20 Feb 2020 at 09:48, Levi Morrison via internals <
internals@lists.php.net> wrote:

> Just chiming in to voice strong support for this RFC. This is a key
> piece toward making PHP code statically analyzable. If it becomes
> required at the call site, such as in an edition of the language, it
> will significantly enhance the ability to reason about code and
> probably make it more correct as well. As a small example, consider
> this method on an Optional type class:
>
> function map(callable $f): Optional {
>   if ($this->enabled) {
>     return new Optional($f($this->data));
>   } else {
>     return $this;
>   }
> }
>
> The intent is to return a new optional or an empty one, but if you
> pass a closure that accepts something by reference you can change the
> original, which is not intended at all. For people who defend against
> it, it requires saving `$this->data` to a local variable, then passing
> in the local. Then if the user does a call-by-reference it will affect
> the local, not the object's data.
>
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>

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