PHP - Unable to implement the same interface twice

Question

I am trying to Implement an interface twice which extends another interface but unable to figure out why i am getting a Fatal Error

Here's my code:

interface a {
    public function foo();
}

interface b extends a {
    public function baz(Baz $baz);
}

// This will work
class c implements b {
    public function foo() {
    }

    public function baz(Baz $baz) {
    }
}

// This will not work and result in a fatal error
class d implements b {
    public function foo() {
    }

    public function baz(Foo $foo) {
    }
}

I am getting this error message:

Fatal error: Declaration of d::baz() must be compatible with b::baz(Baz $baz) in K:\xampp\htdocs\oop\Lec 2\index.php on line 26

Erik · Accepted Answer · 2016-09-14 18:20:01Z

6

Your class d has implemented the baz method incorrectly. The interface specifies it must take an argument with the typehint Baz but you use the typehint Foo - changing the argument type from the interface is disallowed. The fix, in class d, would be:

<?php

class d implements b
{
   public function foo() {}
   public function baz(Baz $foo) {}
}

The function's args are specified by the interface, and may not change.

answered Sep 14, 2016 at 18:20

Erik

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1 Comment

luckyali444 Over a year ago

Thanks @Erik i got it.

Kevin Kopf · Accepted Answer · 2016-09-14 20:39:52Z

1

This is not Java, you can't (unfortunately) overload methods. So, in the end having something like

class d implements b
{
   public function foo()
   {
   }

   public function baz(Foo $foo)
   {
   }

   public function baz(Baz $baz)
   {
   }
}

Will result in

Fatal error: Cannot redeclare d::baz() in [...][...] on line XX

When implementing an interface, you must implement it the same way it is declared. So, since baz is declared with Baz $baz argument, you must implement it with same argument.

class d implements b
{
   public function foo()
   {
   }

   public function baz(Baz $baz)
   {
   }
}

edited Sep 14, 2016 at 20:39

answered Sep 14, 2016 at 18:44

Kevin Kopf

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1 Comment

luckyali444 Over a year ago

I am grateful. It helped @Nordenheim

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