From: Farrel Lifson <farrel.lifson@...>
Date: 2007-03-06T07:37:37+09:00
Subject: Re: [PATCH] Join with block

On 05/03/07, Steven Lumos <steven@lumos.us> wrote:
> Why bother passing sep to the block?

If the block is a pre-existing proc object there's no guarantee it
will have access to whatever is passed to the join method as the
separator.

> Can your implementation handle [1,2,3].join {...} => "1, 2 and 3"?

If the elements in the array are unique it's pretty simple:
  ary = [1,2,3]
  ary.join{|sep,a,b| !ary.last.eql?(b) ? ", " : " and "}

For a case where elements are repeated (but sequences are not):
  ary=[1,2,1]
  ary.join{|sep,a,b| !ary.last(2).eql?([a,b]) ? "," : " and "}

For more complex cases where sequences are repeated ([1,2,1,2]) you're
probably going to need some extra logic:
  ary=[1,2,1,2];idx = 0
  ary.join{|sep,a,b| ((idx+=1) < ary.length-1) ? ", " : " and "}

Farrel