From: dblack@...
Date: 2002-09-24T03:11:55+09:00
Subject: Re: The problem with run-time type checking

Hi --

On Tue, 24 Sep 2002, Brian Denny wrote:

> String and Array are both of type Enumerable, and they both have a "length"

They mix in Enumerable -- which isn't just a quibble about
terminology: the whole mixin process pertains to interface-building
rather than type.

> method.  however, the statement
>
> "String and Array both conform to an (unnamed) type 't', defined as the set
> of those methods which both String and Array objects respond to"
>
> is false, IMO, because the semantics of "each_with_index" are not the same,
> in relation to the semantics of "length", in class String as they are in
> class Array.

They aren't necessarily the same in class String and class String
either :-)

  irb(main):039:0> t
  "hi"
  irb(main):040:0> t.type
  String
  irb(main):041:0> s
  "hi"
  irb(main):042:0> s.type
  String
  irb(main):043:0> t.each_with_index {|x| p x}
  ["hi", 0]
  nil
  irb(main):044:0> s.each_with_index {|x| p x}
  Hello

The dynamic nature of Ruby objects is such that there's really no
guarantee of what they do except... what they do.

That's more of a starting point than an ending point, but I'm almost
late for a class....


David

-- 
David Alan Black                      | Register for RubyConf 2002!
home: dblack@candle.superlink.net     | November 1-3
work: blackdav@shu.edu                | Seattle, WA, USA
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