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.
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