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Date: Fri, 21 Feb 2020 00:26:04 +0100
Cc: php internals <internals@lists.php.net>
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To: Larry Garfield <larry@garfieldtech.com>
Subject: Re: [PHP-DEV] [RFC] Explicit call-site pass-by-reference (again)
From: cschneid@cschneid.com (Christian Schneider)

Am 21.02.2020 um 00:04 schrieb Larry Garfield <larry@garfieldtech.com>:
> On Thu, Feb 20, 2020, at 8:47 AM, Levi Morrison via internals 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:
>>=20
>> function map(callable $f): Optional {
>>  if ($this->enabled) {
>>    return new Optional($f($this->data));
>>  } else {
>>    return $this;
>>  }
>> }
>>=20
>> The intent is to return a new optional or an empty one, but if you
>> pass a closure that accepts something by reference you can change the
>> original, which is not intended at all. For people who defend against
>> it, it requires saving `$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.
>=20
>=20
> If $this->data is itself an object, then you have a concern for data =
manipulation (spooky action at a distance) even if it's passed by value. =
 Given how much data these days is objects, and thus the problem exists =
regardless of whether it's by value or by reference passing, adding =
steps to make pass-by-reference harder doesn't seem to help much.

+1

The whole discussion about being worried about 'malicious' libraries =
altering your precious scalar values misses the fact that PHP is not a =
pure language, there are many ways a function can have side-effects, =
Larry pointing out one obvious one.
Speaking of language editions: Trying to solve one obscure case (and one =
which is easily enough detectable by statical analysis) by introducing =
such a big BC break could render a whole edition ineligible for a =
software project. So beware, features bundled in one (hypothetical) =
edition better not break too many different things at the same time.

If you don't trust your library code then you're in deep trouble anyway.

- Chris