From: Brian Candler <B.Candler@...>
Date: 2004-10-08T01:51:34+09:00
Subject: Re: Range behavior (Re: [RCR] New [] Semantics)

On Fri, Oct 08, 2004 at 01:19:21AM +0900, trans.  (T. Onoma) wrote:
>   - The Ranges #succ can be overridden as either a proc or a an object.
>     If an  object, then each step is simply determined by the addition
>     of that object, i.e. self + #succ. If that succ object is a
>     Numeric, then the range is a numeric range and can gain the 
>     speed advantages of the faster modulo #member? code.

I think more generally, if you provide a proc, then you don't need to
stipulate addition here; the proc could be { |x| x+1 }, or it could be
{ |x| x*2 }

  class DiscreteRange4
    include Enumerable
    def initialize(seed, count, succmeth=:succ)
      @seed = seed
      @count = count
      @succmeth = succmeth
    end
    def each
      val = @seed
      if @succmeth.respond_to?(:call)
        @count.times do
          yield val
          val = @succmeth.call(val)
        end
      else
        @count.times do
          yield val
          val = val.send(@succmeth)
        end
      end
    end
  end

  DiscreteRange4.new(10,5).each { |x| puts x }
  DiscreteRange4.new(10,5,proc {|x| x=x-1}).each { |x| puts x }

(leaving aside that we might want to replace count with an end value or an
end test proc)

So, we've made an iterator generator. I'm not sure how useful this is,
because in these cases it's probably simpler just to write your own
iterator:

  x = 10
  5.times do
    puts x
    x = x-1
  end

Especially where the range is given by a length, and so you can use n.times
{ block } to run it.

Regards,

Brian.