From: Chris Pine <nemo@...>
Date: 2003-04-24T07:18:22+09:00
Subject: Re: [ANN] Ruby.shop

----- Original Message -----
From: "Hal E. Fulton" <hal9000@hypermetrics.com>

I do think that 'a.class == b' and
'a.is_a? b' mean the same thing, though.
(Though you don't mention is_a? above.)
And b.superclass==a does *imply* that
b.kind_of? a (though the converse is not
true).
----------------------------

You should attend my talk if you're going to OSCON!  :)

First off, `is_a?' is aliased to `kind_of?'.

Secondly, this is *not* the same ralationship implied by `class':

  irb(main):001:0> 5.class == Integer
  => false
  irb(main):002:0> 5.kind_of? Integer
  => true

Thirdly, your last statement is false:

  irb(main):001:0> Fixnum.superclass == Integer
  => true
  irb(main):002:0> Fixnum.kind_of? Integer
  => false

In fact, `superclass' and `kind_of?' are fairly loosely related; you can't
call `superclass' on any object, like you can with `kind_of?'.

Might I make a suggestion?  Draw a red line from `a' to `b' if `b' is in
`a.ancestors'.  (This will make the module lines red, also.  Make sure your
lines go the right way; File should point to IO, right?)

This means no red line from Object to Class; yes, `Object.is_a? Class', but
instances of Object don't get any methods from Class.  Use blue lines to
show the `class' relationship (or, if you prefer, the `is_a?' or `kind_of?'
relationship, which is a superset).  My point is, there's a big difference
between the relationships "Fixnum --> Integer" and "Object --> Class".


Chris