Only two things can change self
*Quote from The Ruby Object Model by Dave Thomas.
Paolo Perrotta (*1) answered the question about self in the trial beta course forum.
The point is not whether self has a meaning or not--it always does. The point is when the code is evaluated. Here's an example, slightly edited:
# self_explanation.rb
animal = "duck"
# We're at the top level here, so self is the main object.
self # => main
class << animal
# We just entered the eigenclass (or "singleton class") of animal.
# In here, self is the eigenclass:
self # => #<Class:#<String:0x6194c8>>
# Let's call module_eval() on the eigenclass:
self.module_eval do
# This didn't change self:
self # => #<Class:#<String:0x6194c8>>
# This method is defined as an instance method
# of the eigenclass (a "singleton method").
# The code in the method is not executed until we eventually
# call the method.
def speak_c; self.capitalize; end
end
end
# OK, now let's call speak_c(). In the method,
# self is always the receiver object, so writing
# self.capitalize() is the same as simply writing
# capitalize():
animal.speak_c # => "Duck"
*1: Author of the upcoming Metaprogramming Ruby by the Pragmatic Programmers.
This page was last updated on 20th Dec. 2009.