如果去掉msg code 的风格

demo.cs

class Demo
{
  class Ret<R>
  {
      int error = -1;
      R res;
  }
  interface request { }
  interface response_of<T> { }

  class a_req : request
  {
  }
  class a_res : response_of<a_req>
  {
  }

  delegate void rpc_callback<R>(R r);
  delegate void rpc_call<T, R>(T t, rpc_callback<Ret<R>> f) where T : request where R : response_of<T>;
  
  void rpc_invoke<T,R>(T a, rpc_callback<Ret<R>> f) where T: request where R: response_of<T>
  {
  }

  public void test3()
  {
      rpc_invoke(new a_req(), (Ret<a_res> res) =>
      {

      });
  }
}