Metaclass confusion

Ruby
1

Hi,
can someone explain this.

irb(main):013:0> Class.instance_methods
=> [“superclass”, “new”]
irb(main):014:0> Class.class
=> Class

I guess Class is an object(an instance of Class?) but its of type
Class. How can an object’s type be an object itself.?

Vivek

2

Vivek wrote:

Hi,
can someone explain this.

irb(main):013:0> Class.instance_methods
=> [“superclass”, “new”]
irb(main):014:0> Class.class
=> Class

I guess Class is an object(an instance of Class?) but its of type
Class. How can an object’s type be an object itself.?

The traditional response is ‘magick’ :slight_smile: While it is useful to
say that all instances are Objects and Object is an instance of
class Class which itself is an Object (the class of which is Class),
at some point there has to be a limit to how deep the recursion
goes. Because ruby is implemented in C, the language design allows
this kind of ‘shortcutting’.

To be productive, you sort of just have to accept this and know the
implications of Class being an Object of Class and so on. You can
don some super-chromatic peril-sensitive sunglasses if you like :slight_smile:

Vivek

E

3

On Jan 24, 2006, at 11:28 PM, Vivek wrote:

Vivek

In ruby, everything is an object. Even classes. Class inherits from
object just like everything else (well it inherits from Module which
inherits from Object). Its a little weird to get used to, but that’s
how it works.

4

One implication I have seen is that the class definition itself is an
object which can be executed.This has some interesting properties.

5

Hi –

On Wed, 25 Jan 2006, Eero S. wrote:

Class. How can an object’s type be an object itself.?
don some super-chromatic peril-sensitive sunglasses if you like :slight_smile:
I don’t think any peril is involved (though lately all discussions
seem to lead to talking about shooting in foot, running with scissors,
etc. :slight_smile: It’s just that there’s some circularity at the top of the
class/module hierarchy, for the sake of bootstrapping the whole
system.

David

–
David A. Black
[email protected]

“Ruby for Rails”, from Manning Publications, coming April 2006!

6

Vivek wrote:

One implication I have seen is that the class definition itself is an
object which can be executed.This has some interesting properties.

Umm, in usual terminology objects cannot be “executed”. You can “call”
or
“invoke” methods but you cannot execute an object as such. You probably
meant the right thing - it just sounded quite strange… :slight_smile:

Kind regards

robert
7

On 1/25/06, Logan C. [email protected] wrote:

In ruby, everything is an object. Even classes. Class inherits from
object just like everything else (well it inherits from Module which
inherits from Object). Its a little weird to get used to, but that’s
how it works.

http://redhanded.hobix.com/cult/lastlyTheSinkingSymphonyVideo.html

-Levin

8

A non-circular model would be prototype based inheritance. You just
clone things to subclass them:

Song = Object.new

Song.attr_writer :title
Song.title = ‘No title set’

Song.define_method :play
puts “Playing #{@title}”
end

a_song = Song.clone
a_song.title = ‘Song one’
a_song.play

another_song = Song.clone
another_song.title = ‘Song two’

subclass_of_a_song = a_song.clone
subclass_of_a_song.play

Then there is no distinction between class/object. This is how
Javascript does it, and it seems a good solution.

But we have a class based model, not so clean, but acceptable :wink:

Jules

9

Heh heh, shouldn’t that first line be:

Song = Object.clone

?

10

Hi,

Vivek wrote:

Hi,
can someone explain this.

irb(main):013:0> Class.instance_methods
=> [“superclass”, “new”]
irb(main):014:0> Class.class
=> Class

I guess Class is an object(an instance of Class?) but its of type
Class. How can an object’s type be an object itself.?

The following doc helped me understand Ruby object model pretty well.

Understanding Ruby’s Object Model [ ChrisPine_UROM.ppt ]
(http://www.ruby-doc.org/docs/Understanding%20Ruby’s%20Object%20Model/ChrisPine_UROM.ppt)
at Ruby-Doc.org: Documenting the Ruby Language

Hope this helps.

Sam