From: Yusuke ENDOH <mame@...>
Date: 2011-07-18T14:30:43+09:00
Subject: [ruby-core:38155] Re: [Ruby 1.9 - Feature #4766] Range#bsearch

Hello,

Thank you for all your opinions!


2011/7/18 Michael Edgar <adgar@carboni.ca>:
> This is handy, but what if someone wanted the maximum?

Please invert the condition.  For example, if you want the maximum
index holding that the element is less than 7:

  ary = [0, 4, 7, 10, 12]
  p (0..4).bserach {|i| !(ary[i] < 7) }  #=> 1

Indeed it is not so cool, but similar to Array#sort.  If it is
possible only by inverting, I'm afraid if we need paticular methods
for each use case.


> Or just the first element that matches?

Good question :-)  Interestingly, break can be used.

  ary = [0, 4, 7, 10, 12]
  p (0..4).bsearch {|i| break i if ary[i] >= 4 }
    #=> 1, 2, 3 or 4 (probably 2, but I don't think it might be changed
        in future extension)


> an enumerator for all elements for which the block yields true.

I agree that it seems neat, but it is ambiguous to me how it works
concretely.  What do you expect the following code outputs?

  ary = [0, 4, 7, 10, 12]
  p (0..4).bsearch_matches {|i| ary[i] >= 4 }.to_a #=> ?


And, I guess binary_matches(&blk).min takes O(m) where m is the
number of results because Enumearble#min and #max find the value by
iterating all elements.

-- 
Yusuke Endoh <mame@tsg.ne.jp>