Quoteing eero.saynatkari / kolumbus.fi, on Wed, Jan 26, 2005 at 07:51:57AM +0900:
> > Lett "George  Moschovitis" <george.moschovitis / gmail.com>
> > Aihe: Re: Injecting methods from one class into another.
> > 
> > > I do not think what you want has anything to do with 'duck typing'.
> You're forgetting something. It's not "If it quacks...", it's 
> "If it quacks... and if it walks...". The gist is that as long as
> an object has *all* of the (required) characteristics of a type, the 
> object can be treated as a specimen of that type.

I don't think thats the case at all. I'd like to see you implement
something that "walks like a Hash" by your definition! Make sure you
do all of:

      ==, [], []=, clear, default, default=, default_proc, delete,
      delete_if, each, each_key, each_pair, each_value, empty?, fetch,
      has_key?, has_value?, include?, index, indexes, indices,
      initialize_copy, inspect, invert, key?, keys, length, member?,
      merge, merge!, rehash, reject, reject!, replace, select, shift,
      size, sort, store, to_a, to_hash, to_s, update, value?, values,
      values_at

And there is no "HashWalk" module you can include to make your class
walk like a Hash, so you might have to copy all those methods...

Yet, there are many objects that are sufficiently like a Hash that you
can use that object in place of a Hash, in particular circumstances. I'd
say that's the more common use of duck-typing.

> As an animal analogy regarding 'injecting' methods, tearing off the 
> wings of a duck and gluing them to a pig doesn't mean the pig can fly.

There are methods in library classes I would like in my classes. Right
now, I cut and paste. Yes, if those methods were in a module, I could
include them, but they are not. Would "method stealing" always work? Of
course not. But, the methods I want would work!

This is a real example, the specific methods I have copied are from
resolv.rb, DNS#getaddress() ... DNS#getresources() I have copied (I have
my own #each_resource()).

I may try to inherit. But, my class relationship to DNS does NOT model
a "is a" relationship. So, I am abusing inheritance to steal
implementation. Is this so beautiful?

Also, there are methods I don't want, I need to make sure they do not
appear. Also, there are constants that must have a different value in my
class, can I change them? I don't think so.

Really, I just want those methods!  But, there is no way to get them in
my class other than copying, or convincing the maintainer to cut his
class into pieces for me. Too bad.

Ruby is still better than the alternatives.

Thanks,
Sam