module OptionParser::Completion

def complete(key, icase = false, pat = nil)
  candidates = candidate(key, icase, pat, &method(:each)).sort_by {|k, v, kn| kn.size}
  if candidates.size == 1
    canon, sw, * = candidates[0]
  elsif candidates.size > 1
    canon, sw, cn = candidates.shift
    candidates.each do |k, v, kn|
      next if sw == v
      if String === cn and String === kn
        if cn.rindex(kn, 0)
          canon, sw, cn = k, v, kn
          next
        elsif kn.rindex(cn, 0)
          next
        end
      end
      throw :ambiguous, key
    end
  end
  if canon
    block_given? or return key, *sw
    yield(key, *sw)
  end
end