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Subject: Re: [PHP-DEV] Deprecated partially supported callables: should
 is_callable() throw a deprecation notice ?
From: rowan.collins@gmail.com (Rowan Tommins)

On 02/05/2022 12:56, Alexandru Pătrănescu wrote:
> The point is that this is not an usual deprecation, something that will
> change to an error in the future.
> In the end, it's just a change in behavior with no error before or after.
> It does not fit the "deprecation".


That was my instinct too, but Juliette's analysis elsewhere on the 
thread has convinced me that it is very likely that anyone seeing this 
deprecation would want to change their code, rather than allowing it to 
change behaviour in 9.0.

Perhaps a reasonable comparison is the change in precedence of the 
concatenation operator 
[https://wiki.php.net/rfc/concatenation_precedence]. The expression 
("sum: " . $a + $b) is valid in PHP 7 and PHP 8, but has different 
results; PHP 7.4 included a deprecation notice because users would 
almost certainly want to choose which behaviour they wanted.

The difference in this case is that the code change probably won't 
happen in the same place as the is_callable() function call, but 
somewhere further up the stack. For instance, a framework function might 
accept arbitrary values and test them with is_callable; an application 
using that framework might pass "parent::foo", which will change 
behaviour in 9.0. It is the application's author who will benefit from 
the deprecation notice, so they can pass a different value whose 
behaviour isn't going to change.

Regards,

-- 
Rowan Tommins
[IMSoP]