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To: Stas Malyshev <smalyshev@sugarcrm.com>
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Date: Thu, 19 Aug 2010 10:32:15 +0200
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Subject: Re: [PHP-DEV] inheritance check too strict?
From: johannes@schlueters.de (Johannes =?ISO-8859-1?Q?Schl=FCter?=)

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.

johannes