From: Paolo Nusco Perrotta <paolo.nusco.perrotta@...>
Date: 2007-01-25T04:20:09+09:00
Subject: Re: Trickery in the ancestors chain

Catch-all reply:

On Jan 24, 7:03 pm, "Phrogz" <g...@refinery.com> wrote:
> >But it works as documented. Why do you want to change it?I have two, different responses:
>
> 1) OK, you're right

Yes, it's a feature - I found the C implementation in file class.c,
lines 396 and following (for Ruby 1.8.5). Ruby skips the inclusion of M
in D when D already includes M by way of an ancestor (or itself). This
normally prevents me from adding the same module to the ancestors chain
twice. But I can work around this by including the module in D first,
and later in the ancestor.

I see that most people think this is how it should work. I guess I'm
easily surprised, but I wasn't expecting the order of inclusions into a
hierarchy to make a difference. So, I wonder: why does Ruby go to the
trouble of preventing this in the first place? If it does, shouldn't it
do it all the time, not sometimes? If including a module twice is an
error, shouldn't Ruby raise an exception? I don't have a strong opinion
on this, but it feels strange.