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
    p         


        

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(...).

Answer 2

Following this tutorial, you have no need to use self pointer. But i think this (or self in our case) pointers are used to resolve name conflicts. Actually, @name and self.name are the same statements (if there is no name method for your class). E.g.:

class Moo
  attr_accessor :name

  def moo(name)
    name = name # O_o which *name* should i use?
  end

  def foo(name)
    @name = name # the same as *self.name = name*
  end

  def hello
    puts self.name # the same as *puts @name*
  end
end

a = Moo.new
a.hello() # should give no output

a.moo('zaooza')
a.hello() # Hey! Why does it prints nothing?

a.foo('zaooza')
a.hello() # whoa! This one shows 'zaooza'!

Try running this code and you'll see =)

Answer 3

If you omit self Ruby will first look for local variables with that name, then for an instance method. It's not idiomatic to write self.. In any case, you have to write self.something = value on assignations.

Note that you cannot use self when calling private methods (no problem with protected methods):

class A
  def foo; self.bar; end

private

  def bar; "bar"; end
end

A.new.foo  
# private method `bar' called for #<A:0x7f49193584f0> (NoMethodError)