complete

# File lib/optparse.rb, line 221
    def complete(key, icase = false, pat = nil)
      pat ||= Regexp.new('\A' + Regexp.quote(key).gsub(/\w+\b/, '\&\w*'),
                         icase)
      canon, sw, k, v, cn = nil
      candidates = []
      each do |k, *v|
        (if Regexp === k
           kn = nil
           k === key
         else
           kn = defined?(k.id2name) ? k.id2name : k
           pat === kn
         end) or next
        v << k if v.empty?
        candidates << [k, v, kn]
      end
      candidates = candidates.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