What is self? You may have heard people say that everything in Ruby is an object. If that’s true it means that every piece of code you write “belongs” to some object.
self is a special variable that points to the object that “owns” the currently executing code. Ruby uses self everwhere:
For instance variables: @myvar For method and constant lookup When defining methods, classes and modules. In theory, self is pretty obvious. But in practice, it’s easy for tricky situations to pop up.
Examples of self Inside of an instance method In the code below, reflect is an instance method. It belongs to the object we created via Ghost.new. So self points to that object.
class Ghost def reflect self end end
g = Ghost.new g.reflect == g # => true Inside of a class method For this example, reflect is a class method of Ghost. With class methods, the class itself “owns” the method. self points to the class.
class Ghost def self.reflect self end end
Ghost.reflect == Ghost # => true It works the same with “class” methods inside of modules. For example:
module Ghost def self.reflect self end end Ghost.reflect == Ghost # => true Remember, classes and modules are treated as objects in Ruby. So this behavior isn’t that different from the instance method behavior we saw in the first example.
Inside of a class or module definition One feature of Ruby that makes it such a good fit for frameworks like Rails is that you can execute arbitrary code inside class and module definitions. When you put code inside of a class/module definition, it runs just like any other Ruby code. The only real difference is the value of self.
As you can see below, self points to the class or module that’s in the process of being defined.
class Ghost self == Ghost # => true end
module Mummy self == Mummy # => true end