Multiple ways of calling parent method in PHP

Question

I wasn't sure why both methods calls in the function Object() { [native code] } worked at first, but I think I now understand. Since the methods are passed down from the parent class and are also present in the extending classes, both should function.

Now I'm wondering whether there is a preferred technique (i.e. best practice) of calling the method (through a parent or this), whether these are actually identical ways of running the same code, or if there are any restrictions when using one over the other.

abstract class Animal {

    function get_species() {

        echo "test";

    }

}

class Dog extends Animal {

    function __construct(){

        $this->get_species();
        parent::get_species();

    }

}

$spike = new Dog;

Can someone please help me with this?

Answer 1

There are three circumstances (that I can think of) in which you might call a method in a subclass when the parent class's method exits:

1. The method only exists in the parent and is not overwritten by subclasses. You are correct that in this instance the two are practically the same, but the function has been inherited by the subclass, so there is no reason to differentiate. This is the same as your example, and generally speaking, it's best to use $this -> get species(). You maintain consistency between locally defined methods and inherited methods by using $this.
2. The subclass replaces the method, which uses an entirely different logic from the parent. Given that you don't want the parent's version of the procedure to be used, you should use $this -> get species() in this situation. Again, you can avoid worrying about the difference between this example and the first by continuously using $this.
3. Adding to what the parent method accomplishes, the method extends the parent class. When invoking the method from other methods of the subclass, you should still use "$this -> get species();" in this scenario. Only from the method that is replacing the parent method will you make a call to the parent method. Example:

abstract class Animal {

    function get_species() {

        echo "I am an animal.";

    }

 }

 class Dog extends Animal {

     function __construct(){

         $this->get_species();
     }

     function get_species(){

         parent::get_species();
         echo "More specifically, I am a dog.";
     }
}

I hope this helps you.