Ruby Object's Self

My first experience with object oriented programming came with Java while I was coding in high school. I never learned Java properly, and it wasn’t until working with C++ later on that I got a better understanding of the OOP paradigm.

In Ruby, OOP is implemented in a relatively straightforward way. Classes are defined with the keyword class, which seems unremarkable until you start defining classes in JavaScript. A class serves as a blueprint for your future objects, which you then create instances of, or instantiate, to use in your program.

Here’s some sample ruby code defining a song class.

class Song
  attr_accessor :name, :artist, :genre
  @@all = [] #class variable

  def initialize(name, artist=nil, genre=nil)
    self.name = name
    self.artist = artist if artist != nil
    self.genre = genre if genre != nil
    @@all << self
  end

  def self.all
    @@all #Implicitly returns class array
  end
end

The attribute accessors define and give read/write access to instance variables - variables that are tied to each instance of the class. But in the initialize method, they’re referred to by the keyword self. self is simply a way to refer to the instance itself. So for the actual song object that is created, self.name refers to that specific song’s name.

When self is being pushed onto the @@all class array, self is being used by itself to push that whole object onto the array.

self is also used to define class methods, methods that don’t aren’t a part of instances but the class itself. For example, self.all returns the @@all class array.

The idea of self-referential objects can be tricky if you’re just starting to learn OOP, but it’s necessary in order to build objects that can access their own data.

You can read more about self in the Ruby docs.