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I have created the following simplified working example - where a class Manager takes a template argument and must invoke a member function get_timestamp against the template argument.

class Ex1 {
public:
    int timestamp;
    int get_timestamp() {return timestamp;};
    
};


template<typename T>
class Manager {
    
public:
    void process_data(T& type) {
        
        type.get_timestamp(); // 
    }    
    
};


int main()
{
    Manager<Ex1>();

    return 0;
}

I am looking for a solution where I can replace this type.get_timestamp(); to something like type.FUNC(args); where the FUNC is passed into the class separately. Something similar to passing a lambda or std::function but the difference here is I must instruct the class to treat this "lambda"-like function as a member function of the template argument. Is that possible in C++. I am using c++20

ATK
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  • You can pass the address of `get_timestamp()`, i.e. `&Ex1::get_timestamp`. – Evg Nov 20 '22 at 14:59
  • See [generic member function pointer as a template parameter](https://stackoverflow.com/questions/9779105/generic-member-function-pointer-as-a-template-parameter) – Jason Nov 20 '22 at 15:09

1 Answers1

1

You can pass a member function pointer as a template argument:

template<typename T, int(T::*FUNC)()>
class Manager {
public:
    void process_data(T& type) {
        (type.*FUNC)();
    }
};

Manager<Ex1, &Ex1::get_timestamp> mgr;

Of course you can also pass it as a runtime argument to process_data(), or to the Manager constructor to store as a member variable.

John Zwinck
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  • Actually how do I store it as a variable in the class. – ATK Nov 21 '22 at 08:30
  • Define a type like `using MyFunc = int(T::*)();` in the class and then store `MyFunc func` inside your class instead of passing it as a template argument. – John Zwinck Nov 21 '22 at 18:56