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Date: Wed, 1 Feb 2017 07:49:05 +0100
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To: "Christoph M. Becker" <cmbecker69@gmx.de>
Cc: PHP Internals List <internals@lists.php.net>, Guilherme Blanco <guilhermeblanco@gmail.com>, 
	Levi Morrison <levim@php.net>
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Subject: Re: [PHP-DEV] PHP's support to contravariance and covariance
From: ocramius@gmail.com (Marco Pivetta)

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On 1 Feb 2017 12:27 a.m., "Christoph M. Becker" <cmbecker69@gmx.de> wrote:

On 31.01.2017 at 21:47, Levi Morrison wrote:

>> Is there anything else that I am missing?
>
> Sadly, yes. Consider the following snippet:
>
>     class A {
>         function method(): B;
>     }
>
>     class B extends A {
>         function method(): C;
>     }
>
>     class C extends B {}
>
> When checking that B::method satisfies the requirements of A::method
> it must know if C extends B. At the time we check if B::method
> satisfies A::method, C will *not* yet be in the symbol table.
>
> You need to adjust the passes over the code to register symbols and
> their declared relationships, and then in a separate pass validate
> them. After that if the class isn't found then you trigger an
> autoload.
>
> It's doable, it just hasn't been done.

An alternative *might* be forward class declarations:

    class B extends A;
    class C extends B;

    class A {
        function method(): B;
    }

    class B extends A {
        function method(): C;
    }

    class C extends B {}

I haven't really thought about the feasibility =E2=80=93 just throwing in a
rough idea.


That's simply dumping a language problem onto the user though...

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