From: Dave <dlc-usenet@...>
Date: 2002-01-27T10:13:33+09:00
Subject: Re: Why isn't Range Comparable?

On Sat, 26 Jan 2002 23:28:31 GMT, Niklas Frykholm <niklas@kagi.com>
wrote:

>[Dave]:
>> If a Range is an ordered set, which depends on it's members having
>> '<=>' and succ() methods, then why is there no Range#<=>, so to speak?
>> This simple experiment seems to work fine with a Range of Fixnums, but
>> I haven't tried other object types yet:
>> 
>> irb(main):016:0* class Range
>> irb(main):017:1> def <=>(other)
>> irb(main):018:2> return 0 if self.member?(other)
>> irb(main):019:2> return -1 if other < self.begin
>> irb(main):020:2> return 1 if other > self.end
>> irb(main):021:2> raise "Bogus!"
>> irb(main):022:2> end
>> irb(main):023:1> end
>> 
>> irb(main):025:0> (1..10) <=> 11
>> 1
>> irb(main):026:0> (1..10) <=> 0 
>> -1
>> irb(main):027:0> (1..10) <=> 1
>> 0
>
>(You probably have -1 and 1 inverted above.)

Oops, of course, you're right.


>#<=> is usually used to compare objects of the same class, since ranges
>are not comparable, calling this method #<=> is probably confusing.
>
>I'm not even sure fixnums and ranges of fixnums can always be compared
>in a sane manner. What would you have this return.
>
>    (10..1) <=> 3

Ah, well, I guess I am not really comparing with the range, but with
elements of the range.  I would have (10..1) <=> 3 --> 0, because
regardless of their placement in the Range, that's the way the element
comparison would go.  I'll have to think of a better name for what I'm
getting at.  A sort of a more-informative member? method is what I'm
after.

Speaking of #member?, I was doing some profiling and noticed that it
appears that Range#member? (really Enumerable.member? )
 implemented by iterating through self.each.    I wrote a method based
on the above ideas, and found it much, much faster:

  class Range
          def fastmember?(other)
          return true if ( self.begin <= other && other <= self.end )
          return false
      end
  end

For example, for an input file of 10,000 random alpha strings of
random lengths between 1 and 63 chars, the following ran about 5.5
times faster than using method?

  range = (1..63)
  STDIN.each_line do |string|
       range.fastmember? string.length
  end