| Re: Strange but true! Working with interfaces in PHP [message #185482 is a reply to message #185450] |
Thu, 03 April 2014 14:19  |
Daniel Pitts
Messages: 68
Registered: May 2012
Karma:
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Member |
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On 3/31/14 3:31 PM, Mirco wrote:
> I was working on a software of arbitrary complexity when I stumbled upon this strange behavior of the PHP compiler.
>
> Problem:
> I have these interfaces and classes:
>
> interface IBaseA {
>
> }
>
> interface IA extends IBaseA {
>
> }
>
> interface IBaseB {
>
> public function match( IBaseA $subject );
>
> }
>
> interface IB extends IBaseB{
> }
>
> class A implements IA{
>
> }
>
> class B implements IB{
> public function match( IA $subject ){
> echo "Am I working? o_O<hr>";
> }
> }
>
> $a = new A();
> $b = new B();
> $b->match($a);
>
> Running the above code, this is what I get:
> Fatal error: Declaration of B::match() must be compatible with that of IBaseB::match()
>
> This behavior is very odd, because A implements IA that extends from IBaseA. So IA is an interface of type IBaseA. Methods I will put in IBaseA will be also in IA.
> Class B accepts, in the match() method, an instance of IA.
> Class B extends from IBaseB that in turn accepts an instance of IBaseA.
The error here has nothing to do with "A" or the type of "A". What it is
saying is that "B::match(IA $subject)" is not compatible with
IBaseB::match(IBaseA $subject).
Think about it this way. If I ask for any "IBaseB" object, then I am
expecting to be able to pass in *any* IBaseA object to the match method.
However, your B::match won't accept just any old IBaseA object, but only
ones that implement IA as well.
So this is expected *and* desired.
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