From: matz@... (Yukihiro Matsumoto)
Date: 2003-02-12T03:23:13+09:00
Subject: Re: Range#length?!?!?

Hi,

In message "Re: Range#length?!?!?"
    on 03/02/12, ahoward <ahoward@fsl.noaa.gov> writes:

|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

Interesting.

|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

But 'even this' never reaches 'works quickly' under the current
String#succ behavior.

  for x in 'even this' ... 'works quickly'
    ...
  end

would be an infinite loop.  Do you want to change how it works (to
something doesn't work for multibyte characters)?

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

On the contrary,

  for x in 0.0 ... 42.0
    ...
  end

stops.

							matz.