WDI Darth Vader

Ruby

Classes in Ruby

Scope

1. Defining a class
2. Creating an instance of a class
3. Define what an instance variable is
4. Define what a class variable is
5. Implementing a setter (mutator) and getter

Class: A class is instructions (a blueprint) for building an object. As a class, I can inherit abilities from another class. A class is just an Object.

To create a class, we need to build a skeleton out:

class MyClassName
  #stuff goes here
end

To create a new instance of MyClassName, I would:

my_awesome_class = MyClassName.new()

Each class may have a constructor. That constructor's method name is a reserved word in Ruby called initialize. This constructor can expect arguments passed into the .new() method.

class MyClassName

  def initialize(message)
    puts message
  end

end

my_awesome_class = MyClassName.new("Hello, world!")

If we wanted to create an instance variable for message, we could do so. An instance variable is just a variable assigned to whatever new object created based on each new class. In the following example, we will create an instance variable for message. Instance variables are preceded with @.

class MyClassName

  def initialize(message)
    @message = message #instance variable
  end

end

my_awesome_class = MyClassName.new("Hello, world!")
my_other_class = MyClassName.new("oh, hello friends")

my_awesome_class and my_other_class have two different values for their @message instance variables.

We can also create class variables, variables that apply to all instances of a class. These are not used anywhere near as much as instance variables but may be declared using @@variable_name.

class MyClassName

  def initialize(message)
    @@all_classes_have_me = message #class variable
  end

end

my_awesome_class = MyClassName.new("Hello, world!")
my_other_class = MyClassName.new("oh, hello friends")

Finally, to get/set data in our instance variables, we need to create getter and setter methods. Mutator is another word for setter.

class MyClassName

  def initialize(message)
    @message = message #instance variable
  end

  #getter - calling myClass.message returns @message
  def message
    @message
  end

  #setter - calling myClass.message = "stuff" changes @message
  def message=(new_message)
    @message = new_message
  end

end

my_awesome_class = MyClassName.new("Hello, world!")
my_awesome_class.message # => "Hello, world!"
my_awesome_class.message = "new message"
my_awesome_class.message # => "new message"