From: Robert Dober <robert.dober@...>
Date: 2006-04-11T04:18:15+09:00
Subject: Re: Adding in class attribute with a Module

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On 4/10/06, Gregory Seidman <gsslist+ruby@anthropohedron.net> wrote:
>
> On Tue, Apr 11, 2006 at 02:19:30AM +0900, Robert Dober wrote:
> } On 4/10/06, Gregory Seidman <gsslist+ruby@anthropohedron.net> wrote:
> } >
> } > On Mon, Apr 10, 2006 at 11:58:43PM +0900, TRANS wrote:
> } > } > Is it possible to add class attributes (cattr_accessor) using a
> } > module?
> } > } > If so could you give an example?
> } > }
> } > } There is no "Ruby Way" to do this b/c Ruby's module methods aren't
> } > } inherited by classes that include them. Though I've asked for a way
> } > } man times now!
> } > [...]
> } > } Only ugly meta-programming hacks will give the sought behavior --an=
d
> } > } even then their are corner-case complications.
> } >
> } > Does this count as ugly meta-programming?
> } >
> } > module M
> } >   def self.included(klass)
> } >     class << klass
> } >       attr_accessor :m
> } >     end
> } >   end
> } > end
> }
> } It is much prettier than the following ugly meta-programming, but I hav=
e
> no
> } clue how it works !!!
> } Could you explain please?
>
> The first thing to understand is that when you define a class, e.g. class
> Foo; ... end, you are just setting a constant (Object::Foo, in this case)
> to a new instance of a Class. Just as you can add new methods to an
> instance of any other kind of object with class << obj; ... end, you can
> add new methods to Foo. When a module is included, its self.includedmetho=
d
> is called with the Class instance it is being included into as an
> argument.


I see thank you about the explanation of that hook.

I am defining self.included to add an attribute accessor to that Class
> instance.



No of course not, because it is equivalent to

class <<self
     attr_accessor
end

which does not work.

} Thx
> } Robert
> [...]
> --Greg


Robert




--
Deux choses sont infinies : l'univers et la b=EAtise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

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