Simulate multiple inheritance in PHP

Question

Assuming I have 2 classes

Class A {
    public function doA(){
        echo "Im A";
    }
}
Class B {
    public function doB(){
        echo "Im B";
    }
}

write Class C, in order that the following code runs:

  $c = new C();
  $c->doA();
  $c->doB();

and outputs:

>> Im A
>> Im B

This was in a test, and the conditions where:

use no static calls
you can't modify class A or class B

so I wrote:

Class C {

       public function doA() {
             $a = new A();
             $a->doA();
       }

       public function doB() {
             $b = new B();
             $b->doB();
       }

  }

So apparently I was wrong as it can be "more optimized"

can someone tell me how to do it?

@MatteoTassinari: Never mind, then. :-) I knew you could implement multiple things, I thought you could extend multiple things too. Guess you can't. — gen_Eric
– gen_Eric, Commented Jan 24, 2014 at 17:01

rid · Accepted Answer · 2014-01-24 17:02:21Z

5

You could keep instances of A and B instead of instantiating them each time.

class C {
       private $a, $b;

       public __construct() {
             $this->a = new A();
             $this->b = new B();
       }

       public function doA() {
             $this->a->doA();
       }

       public function doB() {
             $this->b->doB();
       }
}

answered Jan 24, 2014 at 17:02

rid

64k31 gold badges159 silver badges201 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

RicardoE Over a year ago

wooooow nice and easy... :D

Matteo Tassinari · Accepted Answer · 2014-01-24 17:02:00Z

2

PHP has no "native" multiple inheritance, but you can achieve something similar to it by using traits.

Trait A {
    public function doA(){
        echo "Im A";
    }
}

Trait B {
    public function doB(){
        echo "Im B";
    }
}

Class C {
    use A, B;
}

$c = new C;
$c->doA();
$c->doB();

Note that this would require at least PHP 5.4.

answered Jan 24, 2014 at 17:02

Matteo Tassinari

18.6k8 gold badges65 silver badges85 bronze badges

7 Comments

RicardoE Over a year ago

I was not allowed to modify Class A or Class B

Matteo Tassinari Over a year ago

Then go with @rid answer.

ollieread Over a year ago

He can't modify classes A and B, and that's not really the ideal way to use traits.

Matteo Tassinari Over a year ago

Why not, it is just an example though.

ollieread Over a year ago

Because it was a test, and those were the rules specified.

|

ollieread · Accepted Answer · 2014-01-24 17:07:22Z

1

To do it without modifying classes, the best and optimised option would be as follows.

class C {
    private $a;
    private $b;

    public __construct() {
        $this->a = new A();
        $this->b = new B();
    }

    public function __call($method, $arguments = array()) {
        if(method_exists($this->as, $method)) {
            return call_user_func(array($this->a, $method));
        }
    }
}

The above is also future proof, so adding new methods would also follow.

While you were told not to modify classes A and B, the correct way to do this would be by having B extend A, then having C extend B, like below.

class A {
    public function doA(){
        echo "Im A";
    }
}
class B extends A {
    public function doB(){
        echo "Im B";
    }
}
class C extends B {

}

$c = new C();
$c->doA();
$c->doB();

edited Jan 24, 2014 at 17:07

answered Jan 24, 2014 at 17:01

ollieread

6,3211 gold badge22 silver badges36 bronze badges

6 Comments

rid Over a year ago

I'm not sure if that's the "correct" way. It's a way, with advantages and disadvantages (just as __call is not necessarily "the" way, but just a way, again with advantages and disadvantages).

ollieread Over a year ago

Tbh, the question is a rather broad one. Faced with the situation I'd edit classes A & B. There's no reason to not.

RicardoE Over a year ago

well, it was a job interview xD and I got rejected mustly for doing the cascade inheritance thing :(

rid Over a year ago

Sure there is. One big disadvantage is that you'd add a dependency, making B depend on A even if it doesn't have to. Another disadvantage is that you'd get a deeper inheritance tree, making maintenance harder in the long run (the __call approach is much bigger maintenance issue though). The only advantage I see is that you write less code. Again, each way of doing this has advantages and disadvantages, and there's always a reason not to do it one way or another.

ollieread Over a year ago

The problem with job interview tests is that they often pose you with problems you rarely face.

|

Collectives™ on Stack Overflow

Simulate multiple inheritance in PHP

3 Answers 3

1 Comment

7 Comments

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

7 Comments

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related