From: Joel VanderWerf <vjoel@...>
Date: 2008-02-15T15:16:11+09:00
Subject: Re: Cute open range?

Clifford Heath wrote:
> So I wanted to allow folk using my DSL to say "0..N",
> "1..N", etc, to describe the cardinality of a relationship,
> and I needed to find a useful way to define N without
> making it a fixed integer maximum value.
> 
> Well, I came up with this, which I thought was cute:
> 
> class N
>  def self.coerce(n)
>    [ n, n+1 ]    # Anything you can do, I can do better
>  end
> end
> 
> Now when I ask (0..N) === m, for any m, it says "true",
> and when I say the following, it never ends:
> 
> (0..N).each do |n|
>  puts n
> end
> 
> But more importantly, I can say:
> 
> do_something if range.last == N
> 
> Ruby is sweeet :-).

Does that do anything that Infinity doesn't do?

irb(main):001:0> Infinity = 1/0.0
=> Infinity
irb(main):002:0> (0..Infinity) === 3
=> true
irb(main):003:0> (0..Infinity) === -1
=> false
irb(main):004:0> (0..Infinity).each do |n|
irb(main):005:1*   p n
irb(main):006:1>   break if n > 3
irb(main):007:1> end
0
1
2
3
4
=> nil
irb(main):008:0> puts "do_something" if (0..Infinity).last == Infinity
do_something
=> nil


Also, there's this....

class N
  def self.coerce(n)
    [ n, n+1 ]
  end
end

x = 3 + N
p x  # ==> 7   w.t.f.?

Infinity = 1/0.0
x = 3 + Infinity
p x  # ==> Infinity

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407