readme.md

Inheritance in Ruby

Objectives

• Implement inheritance
• Describe what has been inherited from one class to another
• Compare and contrast inheritance in Ruby with Prototypical inheritance in Javascript
• Utilize inheritance to reduce repetition
• Utilize inheritance to model the world
• Install pry using gem. Pry is an improved REPL for Ruby that allows for better debugging and lets you work interactively with pre-written scripts through the use of binding.pry

####Quick Review

1. What is a method? What is a class?
2. What is an instance method?
3. Why do we use a class?

##Inheritance

Inheritance is used to indicate that one class will get most or all of its features from a parent class. Inheritance is useful for a couple reasons.

• DRY - Don't Repeat Yourself & reuse code functionality
• Faster implementation time

###Example

class Rectangle

  def initialize(l, w)
    @length = l
    @width = w
  end

  def get_area
    @length * @width
  end

  def print_shape
    puts "This is a rectangle"
  end

end

class Square < Rectangle
  def initialize(s)
    super(s, s)
  end

  def print_shape
    puts "This is a rectangle and a square"
  end
end

Note from the example above...

• In order to inherit from a class, we use the < keyword and specify the class we want to inherit from
• In order to correctly inherit from Square, we need to call the parent class's initialize method. We can do so by using the super method.
  • If we forget to do this, class and instance variables in the parent will not be initialized
  • When you invoke the super method with arguments, Ruby sends a message to the parent of the current object, asking it to invoke a method of the same name as the method invoking super.
• Once we inherit from another class, we can access methods and properties from the parent. In the case of this Square class, we also overrode the functionality of the print_shape method.

A Guide through Animals

class Animal

  def initialize(kind)
    @kind = kind
    @state = "awake"
  end

  def eat(food)
    if @state == "awake"
      puts "NOM-nom!!"
      puts "(#{kind} has eaten #{food})"
    else
      puts "SLEEPING"
    end
    self
  end

  def sleep
    @state = "sleeping"
    self
  end

  def wake
    @state = "awake"
    self
  end
end

class Person < Animal
  def initialize(age, gender, name)
    super("Human")
    @age = age
    @gender = gender
    @name = name
  end
end

####Single Inheritance vs Multiple Inheritance

• In Ruby, a class can only inherit from a single other class. It cannot inherit from multiple classes.
  • Think about it. What are some benefits and disadvantages to single & multiple inheritance?

####Exercise Create a Mammal class, Cat class, and Dog class. Have Cat and Dog inherit from Mammal. Include some attributes for each class and a method for mammal.