方法调用基类方法后链接派生类方法 [英] method chain a derived class method after calling a base class method

问题描述

具有如下所示的类和派生类，基类方法是否有办法返回派生类型而不是其自身类型的对象引用，因此从语法上讲，我可以将这些方法链接在一起?

With a class and a derivative as shown below, is there a way for the base classes methods to return a object reference of the derived type instead of its own type so syntactically i can chain the methods together?

假设对象 A 具有方法 a1，a2 ，而派生的 AD 添加了方法 ad1 去制作一个有效的方法链 AD_instance.a1().a2().ad1(); ?

Suppose that object A has methods a1,a2 and derivative AD adds a method ad1 how would one go about making a valid method chain of AD_instance.a1().a2().ad1();?

下面是有问题的两个类.忽略它的实际作用，方法链接是唯一重要的部分.

Below are the two classes in question. Ignoring what it's actually doing, the method chaining is the only important part.

class AsyncWorker() {
pthread_t worker;
public:
  AsyncWorker();
  void *worker_run();
  AsyncWorker& Detach() { /*code*/ return *this;  }
  AsyncWorker& Start()  {
     pthread_create(&worker, NULL, &AsyncWorker::worker_helper, this);
     return *this;
  }
  static void *worker_helper(void *context) {
    return ((AsyncWorker *)context)->worker_run();
  }

};

class workerA : public AsyncWorker {
public: 
  int a;
  workerA(int i) { a = i; }
  void* worker_run() { ++a; sleep(1); }
  workerA& other_method_i_want_to_chain() { return *this };
};

像这样被束缚.

workerA A(0);
A.Start().Detach().other_method_i_want_to_chain();

推荐答案

您可以在派生类中创建合适的重载，该重载分派到基类版本，但返回其自身的对象:

You could create a suitable overload in your derived class which dispatches to the base class version but return an object of itself:

class workerA {
    // ...
    workerA& Start() {
        this->AsyncWorker::Start();
        return *this;
    }
    workerA& Detach() {
        this->AsyncWorker::Detach();
        return *this;
    }
    // ...
 };

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