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Date: Thu, 19 Aug 2010 17:42:26 +0800
Message-ID: <AANLkTimuemT15ALt0EaJJ80XTP-SbPJ1mePUFEAS4i0t@mail.gmail.com>
To: =?ISO-8859-1?Q?Johannes_Schl=FCter?= <johannes@schlueters.de>
Cc: Stas Malyshev <smalyshev@sugarcrm.com>, Dave Ingram <dave@dmi.me.uk>, 
	PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] inheritance check too strict?
From: datibbaw@php.net (Tjerk Anne Meesters)

2010/8/19 Johannes Schl=FCter <johannes@schlueters.de>:
> On Thu, 2010-08-19 at 01:13 -0700, Stas Malyshev wrote:
>> Hi!
>>
>> > I was under the impression that, in order for inheritance to provide
>> > proper polymorphism, overridden methods should share the parent's meth=
od
>> > signature, although they can have additional optional arguments.
>>
>> Your impression is wrong. Overriden method should have _compatible_
>> signature - i.e. accept any argument set that parent object accepted.
>> Nothing requires it to have the same signature.
>
> Let|s take a look at making it one step more complex:
>
> class A {
> =A0 =A0public function foo(Foo $a =3D null) {}
> }
>
> class B extends A {
> =A0 =A0public function foo() {}
> }
>
> class C extends B {
> =A0 =A0public function foo(Bar $a =3D null) {}
> }
>
> Here B::foo() is compatible with A:foo() and as the parameter is
> optional C::foo() is compatible with B::foo(). But C::foo() is no more
> compatible with A::foo().
>
> So I consider the message good and correct.

I suppose, when it comes to optional parameters, one can't rely on the
transitive nature of class extension validity. You would need to
iterate the definition chain of this method until it hits the
signature that actually defines the "type" of the parameter(s) before
throwing any messages. In my opinion as a regular developer, B::foo()
would make a valid signature.

>
> johannes
>
>
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>



--=20
--
Tjerk