From: Peter <Peter.Vanbroekhoven@...>
Date: 2003-11-27T11:05:24+09:00
Subject: Re: Range does not take an Range object.

> class Range
>   alias_method :original_include?, :include?
>
>   def include?(other)
>     return original_include?(other) unless other.is_a?(Range)
>     return other.first >= first && other.last <= last
>   end
>
>   def intersect?(other)
>     return true if include?(other)
>     return include?(other.last) || include?(other.first) || other.include?(first) || other.include?(last)
>   end
> end

It should indeed really be built in, because the presence of exclude_end?
and empty ranges make things really complicated. If I could disregard
these issues, I'd implement intersect? as

  def intersect?(other)
    return last >= other.first && other.last >= first
  end

(I had to do that for an assignment in college once, it's weird but
correct; it basically says self is not all smaller than other, and other
is not all smaller than self.)

But that it's hard is illustrated by the current implementation itself,
e.g.,

  irb(main):001:0> (1...1).max
  => nil
  irb(main):002:0> ("1"..."1").max
  => "1"

which seems inconsistent (the inconsistency is because of an inconsistency
in each). Another funny thing is that

  (1..10000000000).member? 9999999999

takes ages to complete, though

  (1..10000000000).include? 9999999999

completes immediately. Still member? is a synonym for include?, or at
least Programming Ruby says so. But I guess I'm the only one interested in
numbers like 10000000000 :-)

Peter