From: Caleb Tennis <caleb@...>
Date: 2005-09-29T04:18:22+09:00
Subject: Re: Python to Ruby: Two puzzlements...

The one thing that really helped me when I first started learning this a long 
time ago is to make sure you understand the difference between class and 
instance methods.

class Foo
  def Foo.class_m
    #this is the same as "self.class_m"
    "in class method"
  end

  def instance_m
    "in instance method"
  end
end

irb> Foo.class_m
in class method
irb> Foo.instance_m
NoMethodError: undefined method `instance_m' for Foo:Class

irb> a = Foo.new
=> #<Foo:0xb7ca10b8>
irb> a.class_m
NoMethodError: undefined method `class_m' for #<Foo:0xb7ca10b8>
irb> a.instance_m
in instance method

It's all because "a" is of type "Foo" while "Foo" is of type "Class":

irb> a.class
=> Foo
irb> Foo.class
=> Class