From: Bill Barnhill <xmlarchitect@...>
Date: 2006-03-14T23:55:31+09:00
Subject: Re: [RCR] abstract method in Ruby

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Good points both, thanks.

If I have the constraint that objects within a certain group must be able t=
o
respond to the methods that make up behavior X, then what would be the best
way to ensure that?

If my group is represented by a collection then I can check for msg
responding on adding to the collection, but if I have a large number of
methods to check, and several different collections, then I'd rather not
have respond to code in each collection's insertion method.

If I declare a delegate at beginning of class with required methods defined=
,
then as I def those methods later in class the delegate methods will get
replaced, right? Is that then the Ruby way to do this?

The behavior I am aiming for is essentially a 'kind_of?' for duck typing,
which as you pointed out is mixing two opposite philosophies.  But I can se=
e
usefulness of something like pattern_of?..ahh, maybe a light bulb is going
off here. Would this then be the ruby way:
.. patterned_obj.pattern_of?(pattern_obj) that does the following
  .. Gets symbols for public methods on pattern_obj
  .. Check to see that patterned_obj responds to all these methods

Still doesn't check for param count though, but it sounds like that may be =
a
good thing, as Ruby makes nice use of different param types and
counts..example being Hash.each.

--Bill

Bill Barnhill
i-name: xri://=3DBill.Barnhill (For more info:
http://2idi.com/grs/index.php?referral_code=3Dcommunitivity
)

On 3/14/06, dblack@wobblini.net <dblack@wobblini.net> wrote:
>
> Hi --
>
> On Tue, 14 Mar 2006, Bill Barnhill wrote:
>
> > Oops, my apologies, forgot an end in example.
> > Should read
> > class B < A
> >    def initialize
> >       @a =3D "foo"
> >    end
> > end
> >
> > Another though on this is that it would allow us to define message
> > interfaces (aka duck-typing prototypes).
>
> I fear that  "duck-typing prototype" is a contradiction in terms.
> With duck typing, you're dealing with an object: it's all about the
> moment you send the message to the object, and the *absence* of
> concern about where that object came from, what its pedigree is, and
> so forth.  "Message interfaces" suggests a higher-level clustering of
> behaviors.
>
> > On 3/14/06, Bill Barnhill <xmlarchitect@gmail.com> wrote:
> >>
> >> Hmm, just some thoughts.
> >> I think the abstract method idea nice in concept, but implementation
> >> perhaps too Java-ish.
> >>
> >> If I get a chance later this week I'll code this, but for now here's
> how
> >> I'd envision something like this within Ruby code:
> >>
> >> class A
> >>     should_respond_to_behavior  #..options hash describing what to do
> if
> >> msg not
> >>                                                # responded to properly
> >> goes here,
> >>                                                # nice to support YAML
> as
> >> well..
> >>     should_respond_to :foo, :bar =3D> {}, :baz =3D> {:param_count =3D>=
 3}
> >> end
> >>
> >> class B < A
> >>     def initialize
> >>        @a =3D "foo"
> >> end
> >>
> >> B.new
> >> =3Dbegin
> >> At this point the class a checks responses:
> >> .. it expects a response to messages :foo and :bar with any or no
> params
> >> .. it expects a response to baz with three params
> >> .. raises exception if either check fails, or logs, depending on
> >> configuraiton
>
> Having a class police the behavior of its instances after they've
> already been created strikes me as being at odds with some of the
> basic conditions of Ruby runtime -- namely, that objects can change
> and aren't constrained by the circumstances of their creation.  I
> suspect it would also be likely to discourage duck typing.
>
>
> David
>
> --
> David A. Black (dblack@wobblini.net)
> Ruby Power and Light, LLC (http://www.rubypowerandlight.com)
>
> "Ruby for Rails" chapters now available
> from Manning Early Access Program! http://www.manning.com/books/black
>
>

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