From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2012-04-11T23:24:51+09:00
Subject: Re: A Beginner's Question about Metaprogramming

On Wed, Apr 11, 2012 at 3:44 PM, Thufir <hawat.thufir@gmail.com> wrote:
> On Wed, 11 Apr 2012 19:56:27 +0900, Jan E. wrote:
>
>>> No. Singleton methods are methods that exist only for a single object.
>>
>> Well, the singleton methods of a class *are* the class methods.
>
> Can you clarify this?  In Java, class methods are declared with static.
> In ruby, I believe it's @@, but the same upshot.

No, @@ is to define class variables, which is a quite different things
than class methods.

>
> There's a distinction between class methods and methods of a Singleton,
> to my understanding.  Methods on a singleton are regular methods and
> require the Singleton object to be instantiated, but are most definitely
> not static methods.  I'm not sure about Ruby, but in Java you wouldn't
> instantiate a Math object to call Math.sqrt() or whatever, that would be
> nonsensical.  Class methods don't require an instance, while, to the
> contrary, Singleton *is* an instance.  Or, rather, the only instance.
>
> From a usage standpoint, I think it's half a dozen of one, six of
> another, but they're not the same at all.
>
> Please correct any misunderstandings I have.

As Jan said, class methods are singleton methods where the object in
which they are defined is the *class* object. Compare:

a = []
def a.half_size
   size / 2
end

This is a singleton method for that specific array object.

class A
  def self.test
    puts "test method"
  end
end

Here, test is a singleton method for the object that is self in that
context, that turns out to be class A. Remember that in Ruby classes
are objects.

Jesus.