heron/common/src/cpp/basics/callback1.h

/*
 * Copyright 2015 Twitter, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef HERON_CALLBACK1_H_
#define HERON_CALLBACK1_H_

#include <functional>

//
// Sometimes we might want to pass some status or data to the functions being invoked.
// In that case we create CallBack1 instead of a CallBack and do something like this
//   void Routine(int arg, int arg2, CallBack1<int>* cb) {
//     ... some code ...
//     cb->Run(arg2);
//   }
// This way Routine can pass status/data to the CallBack cb without having to worry abt
// its signature or its associated arguments.
// Users can invoke Routine in the following manner
// CallBack1<int>* cb = CreateCallback(void (*func)(int));
//    or
// CallBack1<int> cb = CreateCallback(void (*func)(int, char), 'c');
// Routine(arg, arg2, cb);

template <typename C>
class CallBack1 {
 public:
  // Constructor. Users should use the CreateCallback functions detailed below.
  CallBack1(bool persist, std::function<void(C)> f)
    : persistent_(persist), bind_(f) {}

  virtual ~CallBack1() {}

  // The main exported function
  void Run(C c) {
    // In case of persistent callbacks, the RunCallback might delete itself.
    // In that case after RunCallback returns it is not safe to access
    // the class member persistent_. So make a copy now.
    bool persist = persistent_;
    bind_(c);
    if (!persist) {
      delete this;
    }
  }

  // Return whether the callback is temporary or permanent.
  bool isPersistent() const { return persistent_; }

 private:
  bool persistent_;
  std::function<void(C)> bind_;
};

template <typename C, typename... T>
CallBack1<C>* CreateCallback(void (*cb)(C, T...), T... args) {
  return new CallBack1<C>(false, std::bind(cb, std::placeholders::_1, args...));
}

#endif  // HERON_CLASS_CALLBACK1_H_