inheritance.md

Object Inheritance

Inheritance is used to model one class after another. We would want to do this when two objects share functionality. Often the parent class is more general, the child being more specific. For example, we could have a Bird class with more specific classes that inherit like Penguin and Hawk. A way to describe this is by using the "is-a" phrase: i.e. Penguin is a Bird, Hawk is a Bird.

class Bird

  def talk
    puts "I'm a bird. Kah."
  end
end

class Penguin < Bird

end

In Ruby, we use the < symbol to denote that the class on the left of the < symbol is inheriting behaviors from the class on the right side of the < symbol.

Inheriting Methods

So what do we get when we inherit? We get methods. So in the above the Bird class has a talk method defined. Since all birds talk, our child classes will inherit this method. So now even our Penguin instances will have the talk method.

generic_bird = Bird.new
generic_bird.talk
=> "I'm a bird. Kah."

penguin = Penguin.new
penguin.talk
-> "I'm a bird. Kah."

This is known as implicit inheritance because when we put functionality in the base class (Bird), then all subclasses (Penguin) will automatically get those features.

Overriding Methods

What happens when our classes have different functionality for the same idea? We can override methods from parent classes in the child.

class Penguin < Bird
  def talk
    puts "I'm a bird. Sqwaaa."
  end
end

generic_bird = Bird.new
generic_bird.talk
=> "I'm a bird. Kah."

penguin = Penguin.new
penguin.talk
=> "I'm a bird. Sqwaaa."

In this case, you want to override the functionality that the base class (Bird) provides, with more specific functionality in the subclass (Penguin)

super

It's also possible to use the parent method while also overriding in the child method.

class Hawk < Bird
  def talk
    super
    puts "*soars*"
  end
end

generic_bird = Bird.new
generic_bird.talk
=> "I'm a bird. Kah."

hawk = Hawk.new
hawk.talk
=> "I'm a bird. Kah.
*soars*"

In this case, you want to utilize the behavior that the base class (Bird) provides but augment it with functionality specific to the subclass (Hawk).

bird penguin dog