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Date: Tue, 19 Apr 2016 15:30:36 +0100
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Subject: Re: [PHP-DEV] RFC: Functional Interfaces
From: rowan.collins@gmail.com (Rowan Collins)

Dmitry Stogov wrote on 19/04/2016 15:12:
> I prefer intuitive concepts, that I may use without rereading manual 
> again and again.
> For this one, I even can't imagine a natural (not over-designed) use 
> case. 

The use case that came to my mind is kind of the other way around from 
"syntax sugar for anonymous classes" - providing a contract for what a 
callback should look like. In essence, it's an alternative to specifying 
closure type with a generic-like syntax, as proposed at 
https://wiki.php.net/rfc/callable-types

Say you currently have this:

public function registerCallback(callable $callback) { ... }

You could instead specify what the callback needs to accept and return:

interface EventCallbackInterface {
     public function __invoke(Event $event): boolean;
}
public function registerCallback(EventCallbackInterface $callback) { ... }

Using __invoke as the method name may or may not be a good idea, but it 
interestingly means I don't need to change the code that runs the 
callback, I can just use $callback($some_event); Then if someone wants 
to use a complex object, they can; and if they just want to use a 
closure, it has to meet the contract.

Regards,
-- 
Rowan Collins
[IMSoP]