To use self. or not.. in Rails

Question

I\'ve been coding in Ruby for sometime now, but I don\'t understand when to use:

def self.METHOD_NAME
end

or just:

def METH         


        

Answer 1

A quick explanation of what that means:

In ruby, you can define methods on a particular object:

a = "hello"

def a.informal
  "hi"
end

a.informal
=> "hi"

What happens when you do that is that the object a, which is of class String, gets its class changed to a "ghost" class, aka metaclass, singleton class or eigenclass. That new class superclass is String.

Also, inside class definitions, self is set to the class being defined, so

class Greeting
  def self.say_hello
    "Hello"
  end
  #is the same as:
  def Greeting.informal
    "hi"
  end
end

What happens there is that the object Greeting, which is of class Class, gets a new metaclass with the new methods, so when you call

Greeting.informal
=> "hi"

There's no such thing as class methods in ruby, but the semantics are similar.