Must I use lambda to pass a member function as std::function?-CodePudding

The following code works, but I feel that the line worker([this](int a, long b, int* c){receiver(a, b, c);}); is sort of redundant because it is repeating the signature of receiver. Instead of passing a lambda function that in turn calls the member function, can I somehow pass the member function directly?

using callback = std::function<void(int, long, int*)>;

void worker(callback c)
{
    c(1,2L,(int*)3);
}

class Caller
{
public:
    Caller()
    {
        worker([this](int a, long b, int* c){receiver(a, b, c);});
    }

    void receiver(int a, long b, int* c)
    {
    }
};

CodePudding user response：

If you have access to C 20, use bolov's answer. If not…

Though this still uses a lambda, you can take advantage of an argument pack to avoid duplicating the signature:

worker([this](auto... params) { receiver(params...); });

This requires C 14 or newer.

Perfect forwarding can be added if you have more complex types and want to avoid copies:

worker([this](auto&&... params) {
    receiver(std::forward<decltype(params)>(params)...);
});

CodePudding user response：

std::bind is the classical approach, that avoids the need to explicitly spell out the forwarding signature:

using namespace std::placeholders;

// ...

    worker(std::bind(&Caller::receiver, this, _1, _2, _3));

C 20 also has std::bind_front; it reduces this verbiage, somewhat.

You cannot pass a pointer to a member function "directly". This is because a member function requires a specific instance of an object whose member function should get invoked. So, in some form of fashion, in some way, you cannot avoid this, or some other instance of the object, to be involved in the process. This is fundamental to C . The only thing that can be done here is to find some syntactic sugar, which is basically all this is, here.

CodePudding user response：

The cleanest way is C 20's std::bind_front:

worker(std::bind_front(&Caller::receiver, this));

Why use `std::bind_front` over lambdas in C 20?