From: Niklas Frykholm <niklas@...>
Date: 2002-01-27T08:22:52+09:00
Subject: Re: Why isn't Range Comparable?

[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.)

#<=> 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

// Niklas