Ruby OOP Topics

What is a class?

It is a blueprint to create multiple objects of the same type. Its like a template

How do you define a class?

class Person
end

What is an instance?

A single object created from a class definition

How do you create a class instance?

employee = Person.new

How do you add a behavior to a class?

With a method, to access this behavior you would create an instance and call the method

What are attributes?

Values that persist inside an instance of a class, help with maintaining state

How do you store attributes?

Inside the instances, we use instance variables, because instance variables are persist throughout the instance

What is an Object?

It is a way to structure your code, it contains two things: data(attributes), logic(methods).

How does OOP work?

Encapsulation: Used to hide data from outside an object, data(attributes) and methods that work on are bundled together in one unit.

class Person
     def initialize(name)
       @name = name          -> Instance variable 
     end
end
employee = Person.new("Tom")
employee

If you need to access the instance variable create a method and call it

class Person
     def initialize(name)
       @name = name          -> Instance variable 
     end
     def name
       @name                -> can access data inside object
     end
end
employee = Person.new("Tom")
employee.name => "Tom"

I do not like this pattern, I feel like a getter and setter are needed

class Person
     def initialize(name) => 
       @name = name
     end
     def get_name
       @name
     end
     def set_name=(name)
       @name = name
     end
end
employee = Person.new

This pattern is not any better because the initialize method sets the initial value for an object, no need for set_name. Lets test out attr_accesor.

class Person
  attr_accessor :name
  def initialize(name)
    @name = name
  end
  def set_name=(name)
    @name = name
  end
  def get_name
    @name
  end
end
employee = Person.new("Tom")

By using the attr_accessor you can set instance variables outside of the class.

class Person
  attr_accessor :name
  def initialize(name)
    @name = name
  end
end

So what is attr_accessor doing it is creating getter and setter method behind the scenes but how do you check.

class Person
  attr_accessor :name
  def initialize(name)
    @name = name
  end
end
employee = Person.new
puts employee.public_methods => name, name= 

If you would like to learn more Andrew Livingston posted a great article about how attr_accessor works.

Diving Into Ruby’s attr_accessor

What is inheritance?

Permits code resusability by specifying common traits for different objects using parent child or is-a relationship.

What is the parent child relationship and how does it relate to superclass and subclass?

The superclass is the parent and the subclass is the child, the subclass can call a superclass method using the super keyword

Lets expand on the Person class when are been working with and see how inheritance works.

class Person
  attr_accessor :name, :age
  def initialize(name, age)
    @name = name
    @age = age
  end
  def description
    name + " is " + age.to_s + " years old"
  end
end
class Child < Person
  attr_accessor :hobbies
  def initialize(name, age, hobbies)
    super(name, age)
    @hobbies = hobbies
  end
  def get_hobbies
    name + " hobbies are " + hobbies
  end
end
tom = Child.new("Tom", 25, "soccer")
tom.description

What is Duck Typing?

Duck types rely on common interfaces rather than inheritance

class Friend
  def name
    "Chris"
  end
end

class Child
  def name
    "John"
  end
end

class Father
  def greeting(person)
    "Hi #{person.name}"
  end
end

Two completely different types are present but they respond to the same message