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Date: Wed, 12 Nov 2014 11:44:10 +0400
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To: Levi Morrison <levim@php.net>
Cc: internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Re: [RFC][Vote Cancellation] Return Types
From: dmitry@zend.com (Dmitry Stogov)

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On Fri, Nov 7, 2014 at 7:20 PM, Levi Morrison <levim@php.net> wrote:

> > A bug was discovered in the implementation of the return types RFC[1]
> > that cannot be fixed by the current implementation. A strategy for
> > fixing the bug has been identified but alters some noticeable behavior
> > in PHP-land. I do not want people to feel like I did a bait-and-switch
> > move during voting phase, so I have cancelled the vote while this
> > issue is being fixed. More information about the bug and the strategy
> > for fixing it will be published soon.
>
> Here is some more information on the bug:
>
> The following code does a covariance check on B::foo(), because it
> needs to ensure that C is compatible with its parent method A::foo(),
> which returns a B. However, C does not exist at the moment that the
> check is performed and an error is emited saying that it could not
> find class C. If these were split into separate files and autoloaded
> the current solution would work.
>
> <?php
> class A {
>   function foo(): B {}
> }
> class B extends A {
>   function foo(): C {}
> }
> class C extends B {
>   function foo(): C {}
> }
>
> Note that parameters do not have this issue because they are
> invariant, meaning that inheritors have to exactly match the parent
> type. I feel that covariance is a necessary feature for return types
>

It's not especially necessary.
C# uses invariant return types.

Thanks. Dmitry.


> to work, so the voting has been cancelled while this is fixed.
>
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