From: jjenning@... (jared l. jennings)
Date: 2001-07-24T09:11:10+09:00
Subject: [ruby-talk:18397] Re: interfaces?

On Tue, Jul 24, 2001 at 08:49:16AM +0900, MikkelFJ wrote:
> shape_collection.each do  |obj|
>     case obj
>         when IRayIntersection
>             clip_using_interface(obj)
>         when Box
>             clip_as_rectangle(obj)
>         when Sphere
>             clip_as_circle(obj)
>         end
> end

umm, can you just give everything a clip method? i don't see why not. i think the reason has to do with this intersection thing. anyway read on.

> Being able to query for a block of functionality i.e. an interface or a
> module, is important because it has the same advantages as inheritance, but
> goes beyond the limitations of single inheritance, and doesn't have the
> problems of multiple inheritance.

Well, look at this.

jaredj@cobalt:~$ cat foo.rb

class Foo
    def bar
        print "bar\n"
    end
    def baz
        print "baz\n"
    end
end

module Mix
    def baz
        print "mixed!\n"
    end
end

f = Foo.new
f.bar
f.baz
f.extend Mix
f.bar
f.baz
print "f is a Foo!\n" if f.is_a? Foo
print "f is a Mix!\n" if f.is_a? Mix

jaredj@cobalt:~$ ruby foo.rb
bar
baz
bar
mixed!
f is a Foo!
f is a Mix!

> To the earlier discussion on design by contract, one could add the concept
> of contract to class by mixing in a module that ehh "doesn't exist". It's
> just a contract, which the object promises to support. Of it doesn't you get
> a runtime trying to access on of its expected methods.
> You could then do some fancy iterations over contracts: for each object in
> the collection supporting this contract....
> collection.each_contract(AContract) { ... }
> or
> collection.each_module(AModule) { ... }
> 
> Mikkel

if you were to make such contract-modules, you could also go like:

supporting = collection.find_all {|thing| thing.is_a? ContractModule }
supporting.each { ... }
-- 

Doubt is a pain too lonely to know that faith is his twin brother.
- Kahlil Gibran