Joel VanderWerf
10/30/2004 4:35:00 AM
William Morgan wrote:
> Hi all,
>
> I'm currently drowning in a pool of instance_methods and define_methods
> and I can't seem to get out. I know there's an elegant solution
> somewhere....
>
> I have a Class object klass. It has an instance method meth(). I'd like
> to "extend" meth() so that when it's called, the output is changed---I
> want to call the original meth(), tweak its result, and then return it.
> I need to return a Class object that has this tweak in place; I can
> either change klass and return that or I can subclass it and return the
> subclass.
>
> Something like:
>
> def tweaked_class(klass)
> old_meth = klass.instance_method(:to_html)
> klass.define_method(:meth) do |*a|
> r = old_meth(*a)
> # ... transform r ...
> r
> end
> klass
> end
>
> But that doesn't work, and I might be on the wrong track completely.
> So what's the best way to do this?
>
> Thanks,
>
Here are two ways. There are probably more, knowing ruby :)
def tweak(klass, old_meth, new_meth)
if old_meth == new_meth
old_meth_unbound = klass.instance_method(old_meth)
klass.class_eval do
define_method(new_meth) do |*args|
yield old_meth_unbound.bind(self).call(*args)
end
end
else
klass.class_eval do
define_method(new_meth) do |*args|
yield send(old_meth, *args)
end
end
end
klass
end
class Foo
def whazzup; "nothing"; end
end
tweak(Foo, :whazzup, :whaddaya) do |r|
r + " much"
end
p Foo.new.whaddaya
tweak(Foo, :whazzup, :whazzup) do |r|
r + " else"
end
p Foo.new.whazzup