Class Method & Singletons - newbie question

ruby-talk
1

Dear Freinds,

Class Method and Singletons are the same?

Can you explain me with some simple code.

Many thanks in advance,

regards,
salai.

2

Class Method and Singletons are the same?

No, not quite.

Can you explain me with some simple code.

It's very simple. There are really no class methods; there are only
instance methods. It is convenient to talk about class methods, but in
Ruby things are very elegant: a class is itself an instance (of the
Class class), and so a "class method" is merely an instance method of
that instance (i.e. an instance method of an instance of the Class
class).

Okay, so when you define a class method by saying

class C
end
def C.my_method
end

...you are doing EXACTLY the same thing that you are doing when you
define an instance method on any individual instance:

thing = Object.new
def thing.my_method
end

Exactly WHAT same thing? You are opening the instance and defining an
instance method applicable to that instance only. That is the
"singleton". So when you define a class method you are actually creating
a singleton instance method on that Class instance.

m.

PS By the way, in a completely different context (a proposed book about
rb-appscript) I have written an "introduction to Ruby" chapter that
might help you with these concepts. It's here:

http://www.apeth.com/ruby/02justenoughruby.html

Hope this helps.

···

salai <sayakyi@gmail.com> wrote:

--
matt neuburg, phd = matt@tidbits.com, Matt Neuburg’s Home Page
Leopard - http://www.takecontrolbooks.com/leopard-customizing.html
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3

Hi matt,

thanks you very much for your explanation and your "Ruby introduction"
book link.
http://www.apeth.com/ruby/02justenoughruby.html

regards,
salai

···

On Wed, Jun 3, 2009 at 7:55 PM, matt neuburg<matt@tidbits.com> wrote:

salai <sayakyi@gmail.com> wrote:

Class Method and Singletons are the same?

No, not quite.

Can you explain me with some simple code.

It's very simple. There are really no class methods; there are only
instance methods. It is convenient to talk about class methods, but in
Ruby things are very elegant: a class is itself an instance (of the
Class class), and so a "class method" is merely an instance method of
that instance (i.e. an instance method of an instance of the Class
class).

Okay, so when you define a class method by saying

class C
end
def C.my_method
end

...you are doing EXACTLY the same thing that you are doing when you
define an instance method on any individual instance:

thing = Object.new
def thing.my_method
end

Exactly WHAT same thing? You are opening the instance and defining an
instance method applicable to that instance only. That is the
"singleton". So when you define a class method you are actually creating
a singleton instance method on that Class instance.

m.

PS By the way, in a completely different context (a proposed book about
rb-appscript) I have written an "introduction to Ruby" chapter that
might help you with these concepts. It's here:

Just Enough Ruby

Hope this helps.

--
matt neuburg, phd = matt@tidbits.com, Matt Neuburg’s Home Page
Leopard - http://www.takecontrolbooks.com/leopard-customizing.html
AppleScript - http://www.amazon.com/gp/product/0596102119
Read TidBITS! It's free and smart. http://www.tidbits.com