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Date: Fri, 18 Mar 2022 14:37:36 +0100
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To: Juliette Reinders Folmer <php-internals_nospam@adviesenzo.nl>,
 PHP internals <internals@lists.php.net>
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Subject: Re: Deprecated partially supported callables: should is_callable()
 throwa deprecation notice ?
From: cmbecker69@gmx.de ("Christoph M. Becker")

On 16.03.2022 at 06:52, Juliette Reinders Folmer wrote:

> I've just been looking in detail at the Partially Supported Callables
> deprecation RFC:
> https://wiki.php.net/rfc/deprecate_partially_supported_callables
>
> The RFC explicitly excludes the `is_callable()` function and the
> `callable` type from throwing deprecation notices.
>
>> The |is_callable()| function and |callable| type remain side-effect
>> free and do not throw a deprecation warning. They will continue to
>> accept these callables until support is removed entirely.
>
> While I can fully support this for the `callable` type, I wonder if the
> decision to not throw a deprecation on use in `is_callable()` is the
> right one (though I understand the desire to keep it side-effect free).
>
> Consider these code samples:
>
> =C2=A0 function foo(callable $callback) {}
> =C2=A0 foo('static::method');
>
> This function call not throwing a deprecation is not problematic as in
> PHP 9.0 the function will start throwing a TypeError.
>
> =C2=A0 if (is_callable('static::method')) {
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 static::method();
> =C2=A0 }
>
> The second code sample, however, is problematic, as in PHP 9.0, the
> behaviour of this code will be silently reversed for those callbacks
> which would previously result in `is_callable()` returning true, which
> makes this a potentially dangerous change without deprecation notice.
>
> Would anyone care to enlighten me as to whether this was given due
> consideration ?

Frankly, I don't know.  Apparently, there was almost no discussion about
that RFC.  Part of the reasoning to not raise E_DEPRECATED when calling
is_callable() was likely the typical use case

  $callable =3D =E2=80=A6;
  if (is_callable($callable)) {
      call_user_func($callable);
  }

what would report the deprecation when actually calling the callable.
Not sure what to do regarding your given use case(s).

=2D-
Christoph M. Becker