When to use `self.foo` instead of `foo` in Ruby methods

Question

This is not specific for Rails - I am just using Rails as an example.

I have a model in Rails:

class Item < ActiveRecord::Base

  def hello
    puts "Hello, #{self.name}"
  end
end

(Let's assume that the Item model (class) has a method called name.) When do I need to use self.name and when can I just use name (e.g., #{name})?

Answer 1

1. It is idiomatic to prefer to omit self. when invoking methods; it is generally never needed.

2. You must use self.foo = xxx when calling a setter method, instead of foo = xxx, so that Ruby realizes that you are not trying create a new local variable.

   • Similarly, in the unlikely event that you have an existing local variable do_something with the same name as a method, you must use self.do_something to invoke the method, as just do_something will end up reading the variable.

3. You cannot use self.foo(...) to call a private method; you must instead call just foo(...).