将std函数对象转换回functor结构

Question

In this scenario:

struct Holder {
    std::function<void()> f;
};
struct Functor { void operator()(){ /**/ } };
int main() {
    Holder = { Functor{} };
    //...

Is there a way to later cast f back to a Functor type?

Answer 1

The target member function is std::function 's type-unerasing cast. You'll need to know the target type:

#include <cassert>
#include <functional>

struct Functor { void operator()(){ /**/ } };

int main()
{
    std::function<void()> f = Functor();
    Functor * p = f.target<Functor>();
    assert(p != nullptr);
}