From: Brian Candler <B.Candler@...>
Date: 2004-10-05T22:27:07+09:00
Subject: Re: [RCR] New [] Semantics

On Tue, Oct 05, 2004 at 10:10:12PM +0900, Florian Frank wrote:
> Hmm, i just got another idea, how it would be able to always return 
> true or false
> for non-Float ranges:
> 
> def member?(x)
>   include?(x) and 
> Enumerable.instance_method(:member?).bind(self).call(x)
> end

Hmm, but

  (0..1.0/0).member?(99999999)

would still take an inordinate amount of time. For ranges which start with
integers we can do better:

  def member?(x)
    return false unless include?(x)
    return false if first.kind_of?(Integer) and x.to_i != x
    true
  end

but then this is special-casing.

Incidentally, I realised that treating ranges as enumerable isn't going to
make sense for infinite lower bounds:

  (-1.0/0..100).member?(0)

I suppose the iterator could work backwards in this case. Unfortunately,
Ruby does not define a "pred" or "prev" being the reverse of "succ", so I
can't see a general solution.

I start to feel that ranges of discrete items and ranges of the form
a <= b < c are substantially different...

Regards,

Brian.