Self is a core concept in object-oriented programming languages like Ruby. It refers to the current object, and it’s an essential tool for understanding how objects interact with one another in a Ruby program. In this guide, we’ll take a deep dive into what self is and how to use it in Ruby. We’ll cover topics like disambiguating class variables, defining class-level methods, and other common uses for self. By the end of this article, you’ll have a solid understanding of how self works and how to use it effectively in your own Ruby projects.
Table of Contents
- Disambiguating Class Variables with Self
- Defining Class-Level Methods with Self
- Other Uses for Self in Ruby
- Self vs Itself: What’s the Difference?
- Wrapping Up: Mastering Self in Ruby
Disambiguating Class Variables with Self
In Ruby, instance variables are prefixed with @, while class variables are prefixed with @@. However, if you try to define a class variable inside an instance method, you’ll get an error. For example:
class MyClass
def initialize
@@class_var = "Hello"
end
end
This will give you the error class variable @@class_var not initialized.
To define a class variable within an instance method, you can use self.class_var = “Hello”. This tells Ruby that you are defining a class variable, rather than an instance variable.
Defining Class-Level Methods with Self
In addition to disambiguating class variables, you can also use self to define class-level methods. For example:
class MyClass
def self.class_method
puts "Hello from a class method!"
end
end
This creates a class method called class_method, which can be called on the class itself, like this: MyClass.class_method.
Other Uses for Self in Ruby
There are a few other ways you can use self in Ruby:
- To refer to the current object within instance methods
- To refer to the class of the current object within class methods
- To refer to the singleton class of the current object (a special type of class that is only associated with a single object)
Self vs Itself: What’s the Difference?
It’s worth noting that self and itself are not the same thing in Ruby. Self refers to the current object, while itself is a method that returns the object it was called on. For example:
class MyClass
def say_hi
puts "Hi! I am #{self}"
end
def return_itself
itself
end
end
my_obj = MyClass.new
my_obj.say_hi # prints "Hi! I am #<MyClass:0x00007fa70890f1c0>"
my_obj.return_itself # returns my_obj
Wrapping Up: Mastering Self in Ruby
Self is an important keyword in Ruby that allows you to disambiguate class variables, define class-level methods, and refer to the current object within instance methods. It’s essential to understand how it works in order to effectively use object-oriented programming in Ruby.