From: ahoward <ahoward@...>
Date: 2003-02-12T02:59:31+09:00
Subject: Re: Range#length?!?!?

On Wed, 12 Feb 2003, Gavin Sinclair wrote:

> On Wednesday, February 12, 2003, 2:44:34 AM, Chris wrote:
>
> > What happened to Range#length and Range#size?
>
> They disappeared, amidst some discussion in this group, a little while
> ago.  A search of the archives should help.
>
> The reason was that a range of floats has infinite "length"
> (conceptually, not literally), and a range of strings has an
> expensive-to-calculate length.  So the method doesn't make sense in
> general.

IMHO this makes _perfect_ sense :

  class Range
    def size
      case first
	when String
	  a = i = 0
	  first.reverse.each_byte do |byte|
	    a += byte * (256 ** i) and i += 1
	  end
	  b = i = 0
	  last.reverse.each_byte do |byte|
	    b += byte * (256 ** i) and i += 1
	  end
	  return b - a + (exclude_end? ? 0 : 1)
	when Float
	  return 1.0/0.0
      end
    end
  end

  p ('a' .. 'a').size    # => 1
  p ('a' ... 'a').size   # => 0
  p ('a' .. 'z').size    # => 26
  p ('a' ... 'z').size   # => 25
  p ('aa' ... 'aa').size # => 0
  p ('aa' .. 'ab').size  # => 2
  p ('aa' ... 'ab').size # => 1
  p ('aa' ... 'zz').size # => 6425

  p (0.0 ... 42.0).size  # => Infinity



this length of a String Range is easily calculated by interpreting a string as
a base 256 number, eg:

  'abc' -> 'a'[0] * (256 ** 2) + 'b'[0] * (256 ** 1) + 'c'[0] * (256 ** 0)

which makes it very inexpesive (and entirely accurate) to calculate especially
since the 'normal' String ranges are made up of quite short strings.


p ('even this' ... 'works quickly').size # => 9462642498376336060692356596486


it also seems to make perfect sense for Float Ranges to have size Infinity?
this would suprise no one.

-a


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