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Message-ID: <4C6CF898.5060706@gmail.com>
Date: Thu, 19 Aug 2010 10:25:44 +0100
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To: =?UTF-8?B?Sm9oYW5uZXMgU2NobMO8dGVy?= <johannes@schlueters.de>
CC: Stas Malyshev <smalyshev@sugarcrm.com>, Dave Ingram <dave@dmi.me.uk>, 
 PHP Internals <internals@lists.php.net>
References: <4C6CE273.2070501@sugarcrm.com> <4C6CE604.1010209@dmi.me.uk>	 <4C6CE793.1020601@sugarcrm.com> <1282206735.2561.11.camel@guybrush>
In-Reply-To: <1282206735.2561.11.camel@guybrush>
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Subject: Re: [PHP-DEV] inheritance check too strict?
From: nrixham@gmail.com (Nathan Rixham)

Johannes Schlüter wrote:
> 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 method
>>> 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 {
>     public function foo(Foo $a = null) {}
> }
> 
> class B extends A {
>     public function foo() {}
> }
> 
> class C extends B {
>     public function foo(Bar $a = 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.

what if Bar implements Foo, or Bar extends Foo - surely that should be 
compatible given the inheritance chain.