Re: Implementing interface method with child class in parameter def (Bug #42330)

On Wed, Sep 17, 2014 at 8:52 AM, Christian Stoller <stoller@leonex.de> wrote: > Hello all, > > I hope the subject is not misleading. Please look at the following code: > > <?php > class A { } > > class B extends A { } > > interface C { > function foo(A $a); > } > > class D implements C { > public function foo(B $b) { > > } > } > > This code produces a "Fatal error: Declaration of D::foo() must be > compatible with C::foo(A $a) in /xyz/inheritance.php on line 10" > (see http://3v4l.org/l2M0f). > > I don't get the reason for that behavior (and I could not find any > documentation about that, at least not at > http://php.net/manual/en/language.oop5.typehinting.php). > > I have already found https://bugs.php.net/bug.php?id=42330 but > Derick's > response does not help me and the linked file cannot be accessed > anymore. > > I'd say that it is absolutely legal to define a more specialized > type in a child or implementing class, or would this have any bad > side effects? This is because parameters are not covariant, they are usually invariant or contravariant. Almost certainly you have no clue what that actually means; it's okay, most people don't. Just go read and learn about them and learn for yourself why parameter types are not covariant.