From: "Damián M. González" <lists@...>
Date: 2012-09-16T05:56:44+09:00
Subject: Re: Class variables or class singleton variables?

Jan E. wrote in post #1076183:
> I don't get what you mean. The singleton class of a class is obviously
> not the same as the class itself, so getting different object IDs was to
> be expected.

 Yes. What I did was stupid, but I realized late to edit it.

> Maybe you mean something different? If you wonder why I open the
> singleton class in the original class with "self" instead of outside the
> class with the name: That's both the same, but the first approach is
> less redundant and (in my opinion) more readable. But you should
> actually use "send".

 Understood.

> And again: You cannot define a class instance variable for Foo in the
> singleton class of Foo. Those are two different variables:
>
> class Foo
>   @x = 'Foo'
>   class << self    # or class << Foo
>     @x = 'singleton'
>   end
> end
>
> [Foo, Foo.singleton_class].each do |c|
>   puts "#{c}: @x == #{c.instance_variable_get :@x}"
> end
>
> An instance variable always belongs to a specific object instance (hence
> the name). So if you define @x within the body of the singleton class,
> it will actually belong to the singleton class and not the original
> class.

 Now I know, the class itself is an object which can have instance
variables, and the singleton class of a class is kind of another object
that can have their own instance variables.

 class Foo  >> singleton class Foo
 ---------     -------------------
 @x = 1        @x = 3                #not the same variables

 Thanks for your help, I appreciate it.

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