From: Urabe Shyouhei <shyouhei@...>
Date: 2010-10-07T10:03:01+09:00
Subject: Re: Why does Module#include exclude the module's metaclass?

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(2010/10/07 8:33), John Mair wrote:
> Ok, so my question: is there a theoretical/conceptual reason behind thi=
s
> limitation on modules? or was it just an implementation difficulty?

The former.

1) So-called "class methods" are singleton methods of those Class class i=
nstances.

2) A module's class methods are hence, singleton methods of a Module clas=
s
instance.  To say it in another word, they are instance methods of the
singleton class of such module.

3) So if you want a module inclusion to cause somewhat injecting a module=
's
singleton methods into a class's, there should be this relationship:

+---------+   +---------+
|  Meta A +--->  Meta M |
+----^----+   +----^----+
     |             |
  +--+--+       +--+--+
  |  A  +------->  M  |
  +-----+       +-----+

4) But this is impossible, because Meta M is a class.  A class cannot be
included into another class.


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