Ruby self in layman terms?

Question

When is Ruby self refering to the Object and when is self refering to the Ruby class? Explanations with examples would be great. Not getting my head around this.

Answer 1

Classes are actually objects themselves. Lets say that I have a class Person, this is actually an instance of Class. So you can have self refer to an instance of Article, or you can have self refer to the instance of the class, Article.

In the most simple example I can think of:

class Person
  def initialize
    p "Info about Person Instance"
    p self
    p self.class
  end

  p "Info about Person Class"
  p self
  p self.class
end


person = Person.new

It prints:

"Info about Person Class"
Person
Class
"Info about Person Instance"
#<Person:0x0000010086cf58>
Person

To read more about about self, I highly recommend read this.

Answer 2

My understanding is

• In environments where you are defining class methods or module_functions, self refers to the class/module.
• In environments where you are defining instance methods, self refers to the instance.

For example,

class A
  def method1
    self # => instance of A
  end
  def self.method2
    self # => class A
  endu
  def A.method3
    self # => class A
  end
end

class << A
  def method4
    self # => class A
  end
end

module B
  module_function
  def method5
    self # => module B
  end
end

Exceptions are that instance_eval, instance_exec alter self to the receiver.

Answer 3

I could try to explain it myself, but I think Yehuda Katz does a better job than I would do:

Metaprogramming in Ruby: It’s All About the Self