如何在此给定代码中翻译 ::* 运算符和 member_fn？

Question

据我所知：void (A::*p)() = &A::test_func;表示p是一个指向成员函数void A::test_func()的指针，而std::mem_fn(...)可以用来包装一个指向a的指针成员函数。

但在下面的代码片段中，我无法翻译 void (Handler::*)() 和 Handler::*member_fn 的意思。

class Handler;

std::pair<boost::shared_ptr<Handler>, void (Handler::*)()> cb = job_queue.sync_pop();

void (Handler::*member_fn)() = cb.second;
(cb.first.get()->*member_fn)();

Answer 1

class Handler;

std::pair<                     // a pair consisting of first and second
   boost::shared_ptr<Handler>, // first  - a shared pointer to Handler object
   void (Handler::*)()>        // second - a pointer to the member function of Handler class
cb = job_queue.sync_pop();     // sync_pop() returns such pair, stores it in cb variable

// varaible "member_fn" stores pointer to a member function from the pair
void (Handler::*member_fn)() = cb.second; 

// cb.first.get()->  - dereference pointer to Handler object, say handlerObj
// *member_fn        - dereference the pointer to member function
// (cb.first.get()->.*member_fn())()  - invoke the function stored in member_fn variable
//                                      on handlerObj (just like handlerObj.member_fn();)
(cb.first.get()->*member_fn)();

这会更具可读性：

auto pair = job_queue.sync_pop();
auto function = std::bind(pair.second, pair.first.get());
function();

Answer 2

这正是您在第一段中所描述的意思：

// cb contains a shared pointer to an instance of Handler and a member function of Hander
std::pair<boost::shared_ptr<Handler>, void (Handler::*)()> cb = job_queue.sync_pop(); 

// assign the member function stored in cb.second to a local variable    
void (Handler::*member_fn)() = cb.second; 

(cb.first.get()->*member_fn)(); // call the function stored in member_fn on 
                                // the object held by cb.first

如果这不够干净，您可以找到一个使用标准库类 HERE 的最小示例，它做同样的事情

如何在此给定代码中翻译 ::* 运算符和 member_fn？

How to translate ::* operator and member_fn in this given code?

c++

pointer-to-member

c++11