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Date: Mon, 19 Sep 2011 11:35:47 +0200
Message-ID: <CAH-PCH6eGLyR7u0OHHNeE=a9fZwD0H+MkkTYMEsb1xWEW7L3VQ@mail.gmail.com>
To: Gustavo Lopes <glopes@nebm.ist.utl.pt>
Cc: internals@lists.php.net
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Subject: Re: [PHP-DEV] __constructor parameter limitations.
From: tyra3l@gmail.com (Ferenc Kovacs)

On Mon, Sep 19, 2011 at 10:40 AM, Gustavo Lopes <glopes@nebm.ist.utl.pt> wr=
ote:
> Em Sun, 18 Sep 2011 20:06:31 +0100, Stas Malyshev <smalyshev@sugarcrm.com=
>
> escreveu:
>
>> On 9/18/11 11:23 AM, Nikita Popov wrote:
>>>
>>> to tell you: I need this and that method accepting these and these
>>> arguments to work correctly. If the signature isn't enforced, this
>>> doesn't make sense anymore. You could just as well drop the signature
>>> from abstract method definitions, as it's pointless then.
>>
>> No it is not. The signature tells "this method would accept certain
>> arguments". If you call it with these arguments, it would work. However,
>> there's no promise to never extend the cases where it works - it goes
>> contrary to the whole point of OOP to say "I will never loosen precondit=
ions
>> on my methods".
>
> While this is true, we should be a bit pragmatic here.
>
> If the subclass method specifies less parameters, it is very likely a
> mistake. It's not usual (certainly it's not more frequent than a mistake
> being the case) for arguments to be simply intentionally ignored. In fact=
, I
> don't know of any popular language that implements this type of
> contravariance. Plus, consider the case in which the superclass takes an
> argument by reference:
>
> function increment(&$foo) { $foo =3D $foo + 1; }
>
> It is obvious that in this case a subclass override that takes no argumen=
ts
> cannot possibly satisfy the contract of the original method. That is to s=
ay,
> by ref arguments are also used for postconditions.
>
> That said, I think the only rules worth implementing are:
>
> * Allow arguments with a supertype. For instance, this should give no
> warning:
>
> <?php
> class A {}
> class B extends A {}
> class C { function g(B $b) {} }
> class D extends C { function g(A $a) { } }
>
> * Allow extra parameters with a default value (implemented):
>
> <?php
> class C { function g($a) {} }
> class D extends C { function g($a,$b=3Dtrue) { } }
>

could you check my second(lengthy) mail on this thread?
I also tried to come up with the valid, and invalid signature changes.
I forget to take references into account, so thanks for pointing that out.

--=20
Ferenc Kov=C3=A1cs
@Tyr43l - http://tyrael.hu