S> I'm still confused with class and object and metaclass...
well, try to forget about metaclass.
I'll try to give you a *STUPID* explanation
ruby has only objects, this mean that a class is an object and like any
object it has a class (Class) where are defined its methods.
This mean that, for example, the method ::new is defined in Class,
something like this
class Class
def new(*args, &block)
obj = allocate
obj.send
initialize, *args, &block)
obj
end
end
This work fine, but you see that it exist a problem. If it was easy to
define ::new, it will be more difficult to define ::allocate in the same
way, because Array::allocate is completely different from Hash::allocate
and you don't want to define a method Class#allocate with a big switch and
change this method each time that you introduce a new class
Another problem if that it will be nice if you can define a method
File:
pen, which take a block. You can't define this method in Class
(i.e. Class#open) because this mean that you'll define also Array:
pen,
Hash:
pen and you don't want this.
To solve these 2 problems, ruby associate with each class an object and
when it search a class method it search first in this object then it look
in Class.
Now ruby can work, because
* the method ::allocate will be defined in this special object, and you
still have Class#new
* you can define in the object associated with File, the method :
pen
and only this class will have this method
But a class is a little special because there is inheritence and when you
write
class A < Array
end
you want to re-use, for A, the method ::allocate which was defined in the
special object associated with Array
This mean that for this special object, associated with a class, you want
* the possibility to define method
* the possibility to use inheritence
an object is well adapted to do this, this is precisely a class and
because this class will always be associated with only *one* other object
it will called a "singleton" class
Finally this give this (where (A) is the singleton class associated with
A)
Class < Module < Object
(Class) < (Module) < (Object) < Class
A < Array < Object
(A) < (Array) < (Object)
and you have the schema which is given in object.c
Now, at the beginning, I've said that a class is an object and I've
introduced the singleton class. This mean that you can associate a
singleton class with any object, and this will give methods specifics to
this object, for example
a = []
class << a
def tt
end
end
When ruby will search a method for `a', it will first search in its
singleton class then in its class.
Guy Decoux
