From: "David A. Black" <dblack@...>
Date: 2005-08-04T05:07:52+09:00
Subject: Re: [RCR] array or with non-array

On Thu, 4 Aug 2005, Eric Mahurin wrote:

> --- "David A. Black" <dblack@wobblini.net> wrote:
>
>> class != type.  Type is at the heart of duck-typing; class
>> isn't :-)
>
>
> Huh?  Where do you get that?  Duck-typing is about not caring
> about what the type/class the object is.  Duck-typing in the

Class is irrelevant, but you'd be well-advised to care about what the
type is, or you'll find yourself with a lot of NoMethodErrors :-)

> purest sense is calling the methods of the arguments without
> regard to what the class of the object is.

An object's type is the sum of all of its capabilities.  Duck typing
involves focusing on an object's capabilities -- its type -- and not
worrying about its class.  You also don't have to "worry" about its
type (and I agree with those who say that duck typing does not mean
sticking respond_to? everywhere).  But you are dealing with type --
dealing with it, in the sense of making assumptions about it, writing
code governed by those assumptions, etc. -- and not dealing with
class.

I like Jim Weirich's characterization of Ruby as "a duck-typed
language", because it captures the fact that, in a sense, one is
always doing duck typing in Ruby.  That's also why I always feel
uneasy with meta-concepts like the "duck type" of an object.  What
people sometimes call the "duck type" of an object, I call simply the
type of the object.  Duck typing, in that respect, is a way of
describing an approach to programming that arises very organically
from Ruby.


David

-- 
David A. Black
dblack@wobblini.net