From: Christoph Rippel <crippel@...>
Date: 2001-01-16T07:40:03+09:00
Subject: [ruby-talk:9346] Re: Redefining singleton methods & C - function pointers

"ts" <decoux@moulon.inra.fr> wrote in message
news:200101131757.f0DHv4J04461@orsay1.moulon.inra.fr...
...
>  You write a delegator, *warning* this is just an example not fully tested
>
> pigeon% cat b.rb
> #!/usr/bin/ruby
> module DM
>    CODE = <<-'EOT'
>    for method in singleton_methods
>       next if method == "append_features"
>       mod.module_eval <<-EOS
>       def #{mod.name}.#{method}(*args, &block)
>          begin
>             #{name}.send(:#{method}, *args, &block)
>          rescue
>             $@[0,2] = nil
>             raise
>          end
>       end
>       EOS
>    end
>    EOT
>    def DM.append_features(mod)
>       mod.module_eval <<-EOS
>       def #{mod.name}.append_features(mod)
>          DM.append_features(mod)
>          #{CODE}
>       end
>       EOS
>    end
> end
>
> module A
>    include DM
>    def A.a(a)
>       puts "A.a #{a}"
>    end
> end
>
> module B
>    def B.b
>       puts "B.b"
>    end
>    include A
> end
>
> module C
>    include B
>    def C.c
>       puts "C.c"
>    end
> end
>
> p A.singleton_methods
> p B.singleton_methods
> p C.singleton_methods
> pigeon%
>
> pigeon% b.rb
> ["a", "append_features"]
> ["a", "append_features", "b"]
> ["c", "b", "a", "append_features"]
> pigeon%
>
>
> Guy Decoux
Nice - I definitely keep this one in my archive! I have couple
questions and comments and your solutions starting
with the simplest one why you put the rescue clause?
>          rescue
>             $@[0,2] = nil
>             raise
>          end

You need to add a call to #super  somewhere  otherwise regular
instance_methods are not mixed in. I am sure your are aware
of the fact that this does not work (the mixed in function have the
wrong behavior) for nuance functions like

module A
def A.sm1
      id
end
def A.sm2
    to_s
end
end

The way your  code handles arity is problematic  -  functions  relying
on argument separation like

def  A.s (left,*right)
    p  left
    p   right
end

won't work correctly.  Also right now things do  not work if you
retroactively
add a new singleton methods -  i.e. something like this


include DM
end

module Y
include X
end

def X.s
end

p Y.singleton_methods # []


won't work. To do this you need to change the behavior of
#method_added as well.


Christoph