From: Stefano Crocco <stefano.crocco@...>
Date: 2007-08-23T23:19:01+09:00
Subject: Re: What is the difference between :, ::, . ?

Alle gioved� 23 agosto 2007, Xavier Noria ha scritto:
> On Aug 23, 2007, at 2:56 PM, Stefano Crocco wrote:
> > (remember that classes and modules are usually stored in
> > constants).
>
> Are there exceptions?

You can store a class object in any variable. For example:

* in a global variable

 $cls = Hash
 $cls.new
 => {}

* in an instance variable (the point of the example is @cls, not C, of course)

  class C
   attr_reader :cls
   def initialize cls
     @cls = cls
   end
  end

  c = C.new Array
  c.cls.new
  => []

* in a local variable:

  cls = String
  cls.new
  => ''

I think that the code

class MyClass
end

does two different things: 1) creates an instance of class Class with name 
MyClass; 2) stores this instance in the constant MyClass.

If you call Class.new, you get an anonymous class object which is not stored 
in a constant.

Another interesting example is Struct.new. It returns a class object 
corresponding to the new class, but it doesn't get stored in a constant, 
unless you pass a name to Struct.new or explicitly put it in a constant:

cls = Struct.new :attr1, :attr2
=> #<Class:0xb79cfb8c> #the class is only stored in the local variable cls
Cls = Struct.new :attr1, :attr2 
=> Cls #now the class is stored in the constant S
cls = Struct.new 'Cls', :attr1, :attr2 
=> Struct::Cls #now the class is stored in the constant Struct::Cls

Stefano