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To: Andrea Faulds <ajf@ajf.me>, Dmitry Stogov <dmitry@zend.com>
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Subject: Re: [PHP-DEV] [RFC][Discussion] Return Type Variance Checking
From: rowan.collins@gmail.com (Rowan Collins)

Andrea Faulds wrote on 28/11/2014 10:57:
>> On 28 Nov 2014, at 09:31, Dmitry Stogov <dmitry@zend.com> wrote:
>>
>> I prefer option (3) - invariant return types.
>> Actually, return type compatibility check should follow all the rules for
>> parameter type compatibility check (may be even reuse or share the code).
> No, it shouldn't match parameters, that'd break type safety. What's safe for parameters is the opposite of what's safe for return types. The exception is invariance, which is safe for both.

I think you're both saying the same thing: current implementation of 
parameter checking is invariant, proposal is to make return type 
checking invariant. Thus, for now, it can share the implementation.

Later, covariant returns and/or contravariant parameters could be added, 
at which point the checks would need to be split apart again.