From: Trans <transfire@...>
Date: 2006-04-02T10:58:44+09:00
Subject: Re: Typed Parameters


dblack@wobblini.net wrote:
> Hi --
>
> On Sun, 2 Apr 2006, Trans wrote:
>
> > <blockquote>
> > It's not actually that practical, and such things end up making your
> > code very much like C++ and Java.
> >
> > Ruby is smarter than that. Ruby can do more than that.
> >
> > Think in terms of what your object's required capabilities are instead
> > of pretending that a class indicator is sufficient for that.
> > </blockquote>
> >
> > While I understand you pointr Austin --obviously where talking Duck
> > Typing here. But I think it is interesting to condier that this is some
> > respect antithetical to OOP in general --I mean the reciever _is_ a
> > specific type. And that reacieve detemine the functionality of the
> > method call. It is sort of as if you were progamming in a more
> > traditional functional language and _had_ to specifiy the type of the
> > first argument, but never the remaining.
> >
> >  foofunc(  FooClass foo, clever, smart, stupid )
> >
> > instead of
> >
> >  foo.foofunc( clever, smart, stupid )
>
> It's actually more like this:
>
>    foofunc(object_that_responds_to_foofunc, etc.)
>
> The fact that an object handles a message does not imply its class.
> (I'm transliterating 'type' to 'class' as that seems to be what the
> thread is actually about [as it usually is :-].)

But the class of that object dictates the functionality of that
message. That's my point --it's class based.  A double dispath makes
this very clear:

  class String
    def from( obj )
      # the parameter is type String no matter what
      obj.to( self )
    end
  end

We can even do some fancy dispatching to achieve type parameters:

  class String
    def cool( *args )
      args.shift.cool_string( self, *args )
    end
  end

  class Hash
    def cool_string( str, *args )
      args.shift.cool_string_hash( str, self )
    end
  end

  class Boolean
    def cool_string_hash( str, hsh  )
      p str.class, hsh.class, self.class
    end
  end

  def cool( clever, smart, stupid )
    clever.cool( smart, stupid )
  end

  cool( "a string", { :a=>'hash' }, Boolean.new )

produces

  String
  Hash
  Boolean

but

  cool( 1, 2, 3 )  # => NoMethodError

T.