What exactly is Ruby self

Ruby is an object-oriented langauage, a very powerful one. A Ruby class is an object of class Class. And all method calls in Ruby invoke with a receiver, which is the current object. We can refer to the current object by using keyword self, the same as this in Java in term of meaning but a slightly different usages.

In case you don’t know how to define class methods in Ruby, there are several ways to do it. But the one I prefer is,

class Book
  def self.title
    true
  end

  def title
    true
  end
end

self refers to the object depends on its context. self.title in the above example will be invoked by the (current) object, Book. While title will be invoked by the object, Book.new. Therefore, to determine the value of self, you need to think around where the self resides. I highly recommended you to read the smart summary by Paul Barry. And then you should get the idea what the following code is trying to do 🙂

class SelfStudy
  attr_accessor :name

  def self
    @name
  end

  def self.name
    @name
  end

  def self.name=(name)
    @name = name
  end

  def self.default_name
    self.name = "ClassName"
  end

  def default_name
    self.name = "InstanceName"
  end
end

puts SelfStudy.name
#=> nil
puts SelfStudy.default_name
#=> ClassName

me = SelfStudy.new
puts me.name
#=> nil
puts me.default_name
#=> InstanceName

puts SelfStudy.name 
#=> ClassName
puts SelfStudy.default_name
#=> ClassName

Please note the I just want to play up with self in the above example. So instead of defining @name in self method. As you should already know, you may simply replace it with

@name = nil

And you’d get the same output.