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In-Reply-To: <5D33D73A-6B75-456B-9774-91F71FF450BA@cschneid.com>
Date: Thu, 25 Mar 2021 11:35:32 -0400
Message-ID: <CAKuGYLQ1VLu6MOdomenWt3BT-P3NcuC1dYrcDjE2XBOcxB1YuA@mail.gmail.com>
To: Christian Schneider <cschneid@cschneid.com>
Cc: php internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Auto-capture multi-line closures
 andshortfunctions take 2
From: matthewmatthew@gmail.com (Matthew Brown)

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On Thu, 25 Mar 2021 at 10:23, Christian Schneider <cschneid@cschneid.com>
wrote:

> Am 25.03.2021 um 14:29 schrieb Mark Randall <marandall@php.net>:
> > On 25/03/2021 09:28, Rowan Tommins wrote:
> >> That's not quite what I meant. I meant that you can't say "capture by
> default, but this variable is definitely local".
> >
> > I think if there's one argument against, this would be it, but IMHO it
> is a weakness in PHP as a whole.
>
> I'm not sure if I misunderstand what you're saying but to me it is one of
> the greatest things about PHP that everything is local by default (minus a
> narrow set of well-known and easily enough recognizable things).
>
> > The solution would be adding JS-like let / const statements. Which would
> be a benefit to other things too.
>
>
> I disagree that this is the solution. I think JS had to add var and later
> let because of the unfortunate decision to have C-like scoping rules.
> Making scoping in PHP more complex to be able to repeat this mistake in
> some form seems ill-advised to me.
>
> - Chris
>
> --
> PHP Internals - PHP Runtime Development Mailing List
> To unsubscribe, visit: https://www.php.net/unsub.php
>
>
This is also my feeling. While it's easy to see from the single line

    fn ($x, $y)  => $x + $y + $z

that $z is auto-captured, it's much less easy to see that in

    fn ($x, $y) {
        $x += $y >> 2;
        $y = 2 - $y;
        $z -= 4;
        return $x + $y + $z;
    }

Here's an example of this auto-catpuring multi-line functions in use today:
https://github.com/hhvm/hhast/blob/bb0f0445b2e693270079dcced01a29919d87e955/src/Migrations/IsRefinementMigration.hack#L54-L111
I think that code would be more a little more readable with an explicit
closure
    function($node, $parents) use ($map) {

Lastly, PHP's handling of arrays adds an auto-capturing gotcha:

   fn ($x, $y) {
        $z[] = 1;
        return $x + $y + count($z);
    }

This is valid whether or not $z is defined before the closure.

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