From: Paul Brannan <pbrannan@...>
Date: 2002-11-19T11:26:23+09:00
Subject: Re: ruby-dev summary 18711-18810

On Tue, Nov 19, 2002 at 08:48:01AM +0900, Yukihiro Matsumoto wrote:
> Internal iterator is far simpler, and as powerful as external
> iterator, except for parallel iteration.  I won't buy complexity for
> rarely used parallel iteration.

They are useful for more than just parallel iteration; they are also
useful for complex iteration (e.g. I move to the next element when a
particular event occurs).  In C++ I might write:

  int a[] = { 1, 2, 3, 4, 5 };
  std::vector<int> v(a, a + 5);
  std::vector<int>::iterator it = v.begin();
  while(it != v.end()) {
    std::cout << *it << std::endl;
    if(*it == 3) {
      it = v.erase(*it);
    } else {
      ++it;
    }
  }

which produces:

  1
  2
  3
  4
  5

but my naive solution in Ruby doesn't work:

  a = [1, 2, 3, 4, 5]
  a.each_with_index do |x, idx|
    puts x
    if x == 3 then
      a.delete_at(idx)
    end
  end

(it skips the 4).

Or is there a better way to write this that I am missing?

Paul