From: Robert Klemme <bob.news@...>
Date: 2004-06-09T16:18:40+09:00
Subject: Re: Expressing intent in method calling...


"Richard Kilmer" <rich@infoether.com> schrieb im Newsbeitrag
news:BCEB7E82.B88A%rich@infoether.com...
>
>
>
> On 6/8/04 11:51 AM, "Dave Thomas" <dave@pragprog.com> wrote:
>
> >
> > On Jun 8, 2004, at 9:43, Richard Kilmer wrote:
> >
> >> This is not a continuation of the type thread other than trying to
> >> continue
> >> to discuss the ideas of adding metadata that could be used to help
the
> >> runtime environment of Ruby.  Before anyone says anything, I have
> >> built lots
> >> of Ruby code without this, and the runtime is just fine...think of
> >> this as
> >> exploration. Disregard all the other syntax I wrote on earlier...and
I
> >> do
> >> not care whether something is Hash-like, or is_a? Duck ;-)
> >>
> >>   class Person
> >>     attr_accessor :name
> >>   end
> >>
> >>   def greet(person)
> >>     puts "Hello there #{person.<Person>name}"
> >>   end
> >
> > Isn't this effectively "to_name" or "as_name"?
> >
>
> I am not trying to coerce the object into another representation in
general
> (although in the specific example its like that).  Generally, I am
trying to
> add to the message something more than the message symbol and
parameters...I
> am trying to add the 'meaning' of the message as scoped in the namespace
of
> the provided class/module.

Well, "meaning" is a difficult term with computers.  "meaning" (or
semantic) for a coputer is always syntax.  You just add some kind of
symbol to the method invocation which you could transport otherwise, i.e.
as method argument:

o = Object.new

def o.name(expect=nil)
  case expect
    when :Person
      "Rich"
    else
      to_s
  end
end

Alternatively you could do it a bit more behind the scenes via some Thread
local variable that is set somehow before the invocation:

class Object
  alias :method_missing_old :method_missing
  def method_missing(sym, *args, &b)
    new_sym, ctx = sym.to_s.split(/_/, 2)
    method_missing_old(sym, *args, &b) unless ctx

    (Thread.current[:context] ||= []).push( ctx.to_sym )

    begin
      send(new_sym, *args, &b)
    ensure
      Thread.current[:context].pop
    end
  end

  def called_as?(x)
    c = Thread.current[:context]
    c && c[-1] == x.to_sym
  end
end

o = Object.new
def o.name
  if called_as?(:Person)
    "Rich"
  else
    to_s
  end
end

p o.name
p o.name_Person


>  I am trying to add to the method additional
> semantics of what I am asking from the target object.  I am sending the
> message 'name' with the meaning that 'name' has on a Person object.
That
> receiver may or may not care...answering the way it wants, but right now
I
> cannot express that semantics at all.

As I tried to demonstrate above, you can in fact express that already.
You merey add a new syntactic construct.

Regardless of all these issues, currently I don't see the real advantage
of this concept.  Maybe you can explain a little more thouroughly why you
think it's better than method arguments or something else.

> I guess I am not expressing myself with sufficient semantics ;-)

:-)

Kind regards

    robert