Class.class = class

I understand that when you define a new class it´s an instance of
Class…

class Test
end

So you can treat “Test” as an object and asks its class :

Test.class

Class

Is this Class itself an object ?

Because when i do Class.class, ruby gives me ‘Class’

So is Class an instance of itself? I don´t understand the logic behind
this :frowning:

Thanks

Hi –

On Fri, 17 Jul 2009, Rubynewbie Rubynewbie wrote:

Class

Is this Class itself an object ?

Because when i do Class.class, ruby gives me ‘Class’

So is Class an instance of itself? I don´t understand the logic behind
this :frowning:

Yes; Class is an instance of itself. Also, Object is an instance of
Class… but Class is a subclass of Object.

There’s a bit of circularity at the top of the class/instance diagram,
in other words. It’s all in the interest of bootstrapping the object
model into existence, so that everything fits in: classes (including
Class) are instances of Class; all classes descend from Object; etc.

David

Hi,

Am Freitag, 17. Jul 2009, 20:54:26 +0900 schrieb Rubynewbie Rubynewbie:

Class

Is this Class itself an object ?

Yes, it is:

Test.class.ancestors

=> [Class, Module, Object, Kernel]

Class.class

=> Class

Class.class.ancestors

=> [Class, Module, Object, Kernel]

Bertram

Thanks for the responses…

I´m starting to see the light at the end of the tunnel…

Still…I need to do more experimentation with the language because i
still have that “which came first, the chicken or the egg?” feeling :wink:

On 17 Jul 2009, at 13:25, Rubynewbie 72 wrote:

Thanks for the responses…

I´m starting to see the light at the end of the tunnel…

Still…I need to do more experimentation with the language because i
still have that “which came first, the chicken or the egg?” feeling :wink:

A: the omelette :slight_smile:

Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net

raise ArgumentError unless @reality.responds_to? :reason

So is Class an instance of itself? I don´t understand the logic behind
this :frowning:

Well then you’ll love this:

Class.class
#=> Class

Class.superclass
#=> Module

Class.superclass.superclass
#=> Object

Module.class
#=> Class

Object.class
#=> Class

Object.ancestors
#=> [Object, Kernel]

Kernel.class
#=> Module

So Object and Module are instances of a subclass of themselves, and
Object
inherits from Kernel, which is a Module, a subclass of Object. Fun!

The way this actually works is that a Ruby interpreter will implement
Object
using low-level building blocks, then implement Module and Class on top
of
that, then perform a bunch of voodoo to make Object and Module look
like
first-class Class instances.

Some quick rules on Ruby’s type system that I find helpful:

  • Object is the base type. Everything is an Object.

  • Module is a type of Object that stores Methods. A module contains a
    list
    of methods, and possibly pointers to one or more ‘parent’ modules mixed
    in
    using include.

  • Class is a type of Module that not only stores Methods but can also
    spawn
    new Objects that have the class’s methods. Additionally, classes have
    extra
    inheritance semantics in that subclassing is more restrictive than
    mixins,
    and class methods are inherited when subclassing.

  • Kernel is an instance of Module that stores the core methods common
    to
    all Objects. It is mixed into Object after Module is created, thereby
    adding
    the core methods to all extant objects in the Ruby runtime.

On Jul 17, 2009, at 05:25, Rubynewbie 72 wrote:

Thanks for the responses…

I´m starting to see the light at the end of the tunnel…

Still…I need to do more experimentation with the language because i
still have that “which came first, the chicken or the egg?” feeling :wink:

Object comes first from (object.c):

 rb_cObject = boot_defclass("Object", 0);
 rb_cModule = boot_defclass("Module", rb_cObject);
 rb_cClass =  boot_defclass("Class",  rb_cModule);

In 1.9, it’s BasicObject that comes first.

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