gistfile1.rb

def on(sig, types = nil, &blk)
  sig = Signal.create(sig, types)
  candidates = if is_a? Qt::Object
                 signal_map[sig.symbol]
               end
  if candidates
    if types
      # find candidate with the correct argument types
      candidates = candidates.find_all{|s| s[1] == types }
    end
    if candidates.size > 1
      # find candidate with the correct arity
      arity = blk.arity
      if blk.arity == -1
        # take first
        candidates = [candidates.first]
      else
        candidates = candidates.find_all{|s| s[1].size == arity }
      end
    end
    if candidates.size > 1
      raise "Ambiguous overload for #{sig} with arity #{arity}"
    elsif candidates.empty?
      msg = if types
              "with types #{types.join(' ')}"
            else
              "with arity #{blk.arity}"
            end
      raise "No overload for #{sig} #{msg}"
    end
    sign = SIGNAL(candidates.first[0])
    connect(sign, &blk)
    SignalDisconnecter.new(self, sign)
  else
    observer = observe(sig.symbol, &blk)
    ObserverDisconnecter.new(self, observer)
  end
end