How to pass method and call it with variable number of arguments

Question

I have class CallProtector that is supposed to call method with variable number of arguments which suppose to protect call via mutex, but I can't figure out how could I pass object's method with their arguments. Here what I have so far:

class CallProtector
{
public:

    template<typename F, typename ...Args>
    void callProtectedMethod(F& lambda, Args... args)
    {
        std::lock_guard<std::mutex> guard(m_guard);
        lambda(args);
    }

private:
    std::mutex m_guard;
};

I am trying to use it this way:

class Car
{
public:
    void updateEngine(int engineModelType) {}
};

int main()
{
    Car alfaRomeo;
    CallProtector callProtector;
    callProtector.callProtectedMethod(&Car::updateEngine, 10);

    return 0;
}

But I have compilation error saying

no instance of function template "CallProtector::callProtectedMethod" matches the argument list

Appreciate any help, thanks in advance.

NutCracker · Accepted Answer · 2020-12-22 11:34:06Z

1

Following might work for you:

class CallProtector
{
public:

    template<typename F, typename ...Args>
    void callProtectedMethod(F&& func, Args&&... args)
    {
        std::lock_guard<std::mutex> guard(m_guard);
        func(std::forward<Args>(args)...);
    }

private:
    std::mutex m_guard;
};

and then use it like:

Car alfaRomeo;
CallProtector callProtector;

auto updateEngine = std::bind(&Car::updateEngine, &alfaRomeo, std::placeholders::_1); 
callProtector.callProtectedMethod(updateEngine, 10);

EDIT

Or this would work too:

template<typename F, typename ...Args>
void callProtectedMethod(F&& func, Args&&... args)
{
    std::lock_guard<std::mutex> guard(m_guard);
    std::invoke(std::forward<F>(func), std::forward<Args>(args)...);
}

and then

callProtector.callProtectedMethod(&Car::updateEngine, alfaRomeo, 10);

edited Dec 22, 2020 at 11:34

answered Dec 22, 2020 at 10:22

NutCracker

12.4k5 gold badges51 silver badges74 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Oleg Over a year ago

It is not working for me, says: 'term does not evaluate to a function taking 1 argument'. But we could not just forward all the arguments to the std::invoke? Is that any reason for that? It suppose to be very simple, but I really can't figure out.

NutCracker Over a year ago

what term? i think you are not showing us all the code. It works here which is msvc

Oleg Over a year ago

Thanks, yes, my mistake this code works. But could we avoid doing bind and forward all the arguments?

Oleg Over a year ago

I used this code to make it actually work: std::invoke(std::forward<F>(func), std::forward<Args>(args)...);

rafix07 · Accepted Answer · 2020-12-22 09:34:02Z

1

Since C++17 you can use std::invoke, just forwarding all arguments to it:

template<typename ...Args>
void callProtectedMethod(Args&&... args)
{
    std::lock_guard<std::mutex> guard(m_guard);
    std::invoke(std::forward<Args>(args)...);
}

also if you want to call member function on Car instance, you have to pass pointer to object.

Full demo

answered Dec 22, 2020 at 9:34

rafix07

21.3k3 gold badges26 silver badges36 bronze badges

3 Comments

Oleg Over a year ago

Thank you, but it is not working for me. Compile error says that: 'invoke' no matching overloaded function found. I am using visual studio 2019 with c++ 17. Also could we do the same with c++ 14?

rafix07 Over a year ago

@Oleg Why not to make callProtectedMethod as function accepting any callable object ? Demo, passed callable can be created as closure or result of std::bind function - there is no problem with passing arguments, just call function with protection of mutex.

Oleg Over a year ago

I have to use different objects and pass pointer to it.

Collectives™ on Stack Overflow

How to pass method and call it with variable number of arguments

2 Answers 2

4 Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related