From: Urabe Shyouhei <shyouhei@...>
Date: 2010-10-07T20:21:20+09:00
Subject: Re: Why does Module#include exclude the module's metaclass?

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(2010/10/07 10:59), John Mair wrote:
> 1) I agree that singleton class of the module is actually a 'class' but=
=20
> (if we allowed this behavior) it would only be included when and only=20
> when the module is included. We can just consider this a special=20
> exception, no?
>=20
> This exception would only apply to singleton class of modules, of=20
> course, normal classes cannot be included in this way.

So you were actually not asking why, but claiming this is wrong.  Not sur=
e for
that.  Your real_include gem breaks Class#ancestor in a strange way so I =
guess
there are some pitfalls, though noting particular.

> 2) Given that class inheritance does include the singleton, do you not =

> think it 'surprising' that module inclusion does not? I found it=20
> surprising.

Tips: principle of least surprise is a wrong way for you to persuade matz=

because at any moment he can say "I don't think so".  Try a different rou=
te.

> 3) Many people get around this limitation in module inclusion by abusin=
g=20
> the included() hook and then extending a ClassMethods submodule, I thin=
k=20
> this is ugly.

Maybe.  But I think a module's having class method is itself ugly.  It te=
nds
to smell like a API design mistake.  I would recommend you to rethink why=
 you
need such things.

> 3) Out of curiosity, are there any other reasons (besides the one you=20
> gave) for why modules do not include the singleton? What reason did Mat=
z=20
> give?

No, I do not know other reasons.  It is rather obvious to me.  Of course =
that
does not ensure there is not reason though.


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