From: Trans <transfire@...>
Date: 2006-09-09T07:06:26+09:00
Subject: Re: better alias_method


Ken Bloom wrote:
> On Sat, 09 Sep 2006 02:54:35 +0900, Trans wrote:
>
> > ara.t.howard@noaa.gov wrote:
> >> heh.  i think you may be hitting the same thing i was.  here's some food for
> >> thought:
> >>
> >>
> >> this works:
> >>
> >>      harp:~ > cat a.rb
> >>      class C
> >>        include Module.new{ def m() 'a' end }
> >>        include Module.new{ def m() super + 'b' end }
> >>        include Module.new{ def m() super + 'c' end }
> >>      end
> >>
> >>      p C.new.m
> >>
> >>
> >>      harp:~ > ruby a.rb
> >>      "abc"
> >>
> >>
> >> while this does not:
> >>
> >>      harp:~ > cat a.rb
> >>      class C
> >>        def m() '' end
> >>
> >>        include Module.new{ def m() super + 'a' end }
> >>        include Module.new{ def m() super + 'b' end }
> >>        include Module.new{ def m() super + 'c' end }
> >>      end
> >>
> >>      p C.new.m
> >>
> >>
> >>      harp:~ > ruby a.rb
> >>      ""
> >>
> >> even more distilled:
> >>
> >>      harp:~ > cat a.rb
> >>      class C
> >>        def m() '' end
> >>
> >>        include Module.new{ def m() 'a' end }
> >>      end
> >>
> >>      p C.new.m
> >>
> >>
> >>      harp:~ > ruby a.rb
> >>      ""
> >>
> >>
> >> i find that behviour quite suprising... in fact, it seems like a bug, but i'm
> >> probably wrong...  thoughts?
> >
> > Not at all becasue inclusion adds to the inheritance chain, it doesn't
> > inject methods. You can of course define an #inject method if you like.
> > But it's still difficult to do the orginial intent of this thread b/c
> > of how #super works.
> >
> > Personally I think it would cool if you could redefine a method calling
> > on the previous definition just as one can redefine a variable calling
> > on it's previous definition. Eg.
> >
> >   a = 1
> >   a = a + 1
> >
> >   def a ; 1 ; end
> >   def a ; a + 1 ; end
> >
> > This would eliminate the need for #super except in cases of recursion,
> > in which case a special notation is also needed for the definition. Eg.
> > def_rec a, or something. But that's cool b/c it would be safer.
> >
> > In anycase, alternate solutions to the alias issue include
> > #wrap_method,
>
> see http://www.erikveen.dds.nl/monitorfunctions/index.html#implementation
>
> > #alias_chain, Matz' :before and :after system (semi-aop) and cuts (aop).
>
> Where is there information about these?

All of these can be found in Facets (facets.rubyforge.org) except Matz'
system which is just a concept given in his keynotes. (see
http://www.rubyist.net/~matz/slides/rc2005/mgp00006.html).

Note #alias_chain is actually #alias_method_chain and is borrowed from
Rails. It's quite clever, but has limited usage.

T.