Passing capturing lambda as function pointer

Question

Is it possible to pass a lambda function as a function pointer? If so, I must be doing something incorrectly because I am getting a compile error.

Consider the follo

Answer 1

A simular answer but i made it so you don't have to specify the type of returned pointer (note that the generic version requires C++20):

#include 


template
struct function_traits;

template 
struct function_traits {
    typedef Ret(*ptr)(Args...);
};

template 
struct function_traits : function_traits {};

template 
struct function_traits : function_traits {};

using voidfun = void(*)();

template 
voidfun lambda_to_void_function(F lambda) {
    static auto lambda_copy = lambda;

    return []() {
        lambda_copy();
    };
}

// requires C++20
template 
auto lambda_to_pointer(F lambda) -> typename function_traits::ptr {
    static auto lambda_copy = lambda;
    
    return [](Args... args) {
        return lambda_copy(args...);
    };
}



int main() {
    int num;

    void(*foo)() = lambda_to_void_function([&num]() {
        num = 1234;
    });
    foo();
    std::cout << num << std::endl; // 1234

    int(*bar)(int) = lambda_to_pointer([&](int a) -> int {
        num = a;
        return a;
    });
    std::cout << bar(4321) << std::endl; // 4321
    std::cout << num << std::endl; // 4321
}