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Date: Wed, 16 Mar 2022 06:52:01 +0100
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Subject: Deprecated partially supported callables: should is_callable() throw
 a deprecation notice ?
From: php-internals_nospam@adviesenzo.nl (Juliette Reinders Folmer)

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L.s.,

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:

   function foo(callable $callback) {}
   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.

   if (is_callable('static::method')) {
       static::method();
   }

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 ?

Smile,
Juliette











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