From: David Alan Black <dblack@...>
Date: 2000-12-23T08:37:40+09:00
Subject: [ruby-talk:7983] Re: Naming of "defined?"

On Sat, 23 Dec 2000, Dave Thomas wrote:

> "Guy N. Hurst" <gnhurst@hurstlinks.com> writes:
> 
> > I had a problem on page 221 of Programming Ruby,
> > where it indicates that "defined?" is a method... Dave,
> > could you explain? (Maybe I should have said something sooner)
> 
> You think _you_ had a problem on page 221 ;-)
> 
> Actually, that's a bug. Maybe. We _call_ it an operator consistently,
> and the tick in the method column says that it can be overridden.
> That's only half true. You _can_ override it, but you can't easily
> _use_ the new method:
> 
>   def defined?(a)
>     puts "new"
>   end
>   puts defined?(1)       #=> "expression"
>   public :defined?
>   puts self.defined?(1)  #=> new
> 
> So I'm not sure what to do: shall we remove the tick or not?
> 
> 
> Confused of Dallas
> 

It seems more like an co-ride than an override, at least taking the
latter term in a possibly sub-rigorous, semi-intuitive sense.  You can
certainly do similar things with other things that are not "ticked
off" on p. 221:

   irb(main):001:0> def not
   irb(main):002:1> puts "No way"
   irb(main):003:1> end
   nil
   irb(main):004:0> public :not
   Object
   irb(main):005:0> self.not
   No way
   nil
   irb(main):006:0> not 3
   false
   irb(main):007:0>


... so I'm not sure what defined?'s tick has going for it.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
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