How to reset an std::function?

Question

std::function can be empty, and it's convertible to bool to test if it has a target or not. But, how to set it to null after you've assigned something to it?

int main()
{
    std::function<void()> f = []() { return 4; };
    // how to reset to null, to it's initial state when default constructed.
}

Answer 1

You can either:

• assign nullptr to it:

  f = nullptr;
  

• assign an empty function to it:

  f = std::function<void()>{};
  // or:
  f = decltype(f){};
  

• swap() it with another empty function:

  std::function<void()>{}.swap(f);
  // or:
  decltype(f){}.swap(f);