medium-oop-series-examples-3.rb

class MyClass
  @@my_class_variable = "Class variable content."
  
  def initialize
    @my_instance_variable = "Instance variable content."
  end
  
  # Class methods have a "self." before their name. For now we won't go into the details 
  # on why it is that way.
  def self.thing_my_class_does
    puts "Inside the instance method!"
    puts @@my_class_variable
  end
  
  def thing_an_instance_of_my_class_does
    puts "Inside the instance method!"
    puts @my_instance_variable
  end
end

MyClass.thing_my_class_does
# This will print the following to the screen:
# Inside the class method!
# Instance variable content.

MyClass.new.thing_my_class_does
# This will cause a NoMethodError, since the instance of MyClass does not have such method:
# NoMethodError: undefined method `thing_my_class_does' for #<MyClass:0x0055a389098170>

MyClass.new.thing_an_instance_of_my_class_does
# This will print the following to the screen:
# Inside the instance method!
# Instance variable content.

MyClass.thing_an_instance_of_my_class_does
# This will also cause a NoMethodError, since MyClass does not have such method:
# NoMethodError: undefined method `thing_an_instance_of_my_class_does' for MyClass:Class