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

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(...).

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)