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To: "Dan Ackroyd" <danack@basereality.com>
Cc: "PHP internals" <internals@lists.php.net>
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Date: Sat, 23 Apr 2016 15:35:26 +0300
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Subject: Re: [PHP-DEV][RFC] Callable Types
From: inefedor@gmail.com ("Nikita Nefedov")

On Sat, 23 Apr 2016 14:18:56 +0300, Dan Ackroyd <danack@basereality.com>  
wrote:

> On 22 April 2016 at 05:12, Marcio Almada <marcio.web2@gmail.com> wrote:
>> Hello everyone,
>>
>> We just completed the draft for the "Callable Types" RFC.
>
> There seems to be one thing missing from the RFC; please could you add
> an example where the parameter and return types are also 'typed'
> callables?
>
> Presumably it would look something like this?
>
> function reduce(int $a, int $b, callable(int, callable(int, int):int
> $math):int $reducer): callable(int, int):int {
>   return $reducer($a, $b);
> }
>
> Are there any limits to how far down the callable type can be defined ?
>
> cheers
> Dan

Hey Dan,

thanks for reviewing.

I have just added a paragraph about nested callables, I'll copy paste it  
here:

Nested callables can be used with no imposed limit on the nesting level.

     function foo(callable(callable(int)) $cb) {
         $cb(function (int $i) {
             var_dump($i);
         });
     }

     foo(function (callable(int) $intPrinter) {
         $intPrinter(123);
     });

There's currently no way to reference callable signature from within  
itself, meaning there's no way to make recursive signatures like below:

     function bar(callable(int $number): callable(int $number):  
callable(int $number): parent_callable $recursiveCb) { // this wouldn't  
work currently
     }

To add to that, nested callables can get pretty unreadable quickly, both  
of these problems would be best solved by a typedef feature of some kind,  
added to PHP later.