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Date: Fri, 7 Nov 2014 08:20:20 -0700
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To: internals <internals@lists.php.net>
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Subject: Re: [RFC][Vote Cancellation] Return Types
From: levim@php.net (Levi Morrison)

> 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
to work, so the voting has been cancelled while this is fixed.