Inheritance

In Ruby, inheritance describes the relation between classes.

Inheritance is expressed when the < is used to connect the parent class, Animal, with the child class, Dog:

class Animal
  def initialize(species)
    @species = species
  end

  def species
    @species
  end
end

class Dog < Animal
  def initialize(species, name)
    super(species)
    @name = name
  end
end

snoop = Dog.new("Long-Beach Labrador", "Calvin")

puts snoop.species # Output: Long-Beach Labrador

The Dog class inherits all the methods from its parent Animal class, including .species.

An inheriting child class can override methods defined in its parent and replace with code specific to it:

class Animal
  def initialize(species)
    @species = species
  end

  def species
    @species
  end

  def make_sound
    "The animal made a sound that was hard to tell."
  end
end

class Dog < Animal
  def initialize(species, name)
    super(species)
    @name = name
  end

  def name
    @name
  end

  def make_sound
    "Bark!"
  end
end

snoop = Dog.new("Long-Beach Labrador", "Calvin")

puts snoop.make_sound # Output: Bark!

The .make_sound method from Animal was overridden in Dog with a return string specific to that class.