From: dblack@...
Date: 2007-02-21T12:01:51+09:00
Subject: Re: Range#overlap?

HI --

On Wed, 21 Feb 2007, bbiker wrote:

> On Feb 20, 7:04 pm, dbl...@wobblini.net wrote:
>> Hi --
>>
>>
>>
>>
>>
>> On Wed, 21 Feb 2007, Daniel Schierbeck wrote:
>>> On Wed, 2007-02-21 at 08:00 +0900, Daniel Finnie wrote:
>>>> I think your implementation is cleaner however the endpoints of a Range
>>>> do not have to implement #succ.
>>
>>>> class Range
>>>>    def span? other
>>>>      include? other.first and
>>>>        (other.exclude_end? ? other.last < last : other.last <= last )
>>>>    end
>>>> end
>>
>>> I've tried that implementation, but i doesn't work if you consider this
>>> valid:
>>
>>>  (4..8).span? 6...9
>>
>>> Since 6...9 yields the same values as 6..8. Or am I wrong to expect the
>>> above?
>>
>> I don't think ranges really yield values.  Some of them can be
>> converted to arrays, but a range qua range is really just two
>> endpoints, between which everything comparable to those endpoints
>> either is or isn't.
>>
>> I'm not sure I have my head around what span? is supposed to be doing.
>> Can you write some test cases?  I keep thinking of this:
>>
>>    include?(other.first) and include?(other.last)
>>
>> but I don't think that's what you're trying to do with span?.
>>
>
> Here is my entry for overlap?
> <code>
> require 'facets/core/range/within'
>
> class Range
>
>  # Uses the Range#within and Range#include methods to determine
>  # if another Range _overlap_ this Range.
>  # neither Range is within the other Range
>  #   (1..3).overlap?(2..4)  #=> true
>  #
>  def overlap?(other)
>    #   |---|      |---|   |-----|  |-----|  |-----|
>    #   |-----|   |-----|  |-----|   |---|     |---|
>    !self.within?(other) && !other.within?(self) &&
>    #  |-------|    |------|
>    #   |-------|          |-------|
>    (self.include?(other.first) && other.include?(self.last) ||
>    #   |-------|          |-------|
>    #  |-------|    |------|
>     other.include?(self.first) && self.include?(other.last))
>  end
> end
>
>
> =begin test
>
>  require 'test/unit'
>
>  class TCRange < Test::Unit::TestCase
>
>    def test_overlap?
>      assert(!(3..6).overlap?(3..6) )
>      assert(!(4..5).overlap?(3..6) )
>      assert(!(2..7).overlap?(3..6) )
>      assert( (2..5).overlap?(3..6) )
>      assert( (2..3).overlap?(3..6) )
>      assert( (7..10).overlap?(6..9) )
>      assert( (9..12).overlap?(6..9) )
>    end
>  end
> =end
> </code>

Here's a slightly shorter method that makes all the tests pass:

     def overlap?(other)
       self.include?(other.first) &&! self.include?(other.last) or
       other.include?(self.first) &&! other.include?(self.last)
     end


David

-- 
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
    (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)