lib/moveonlyfunction.cpp

The following code example is taken from the book
C++23 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2026
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <functional>

int cube(int i) {
  return i * i * i;
}

void callMO(std::move_only_function<int(int)> f) {
  if (f) {
    std::cout << f(7) << '\n';
  }
}

int main()
{
  std::move_only_function<int(int)> mofunc;

  mofunc = cube;                        // refer to ordinary function
  callMO(std::move(mofunc));
  callMO(cube);

  mofunc = std::negate<int>{};          // refer to function object
  callMO(std::move(mofunc));
  callMO(std::negate<int>{});

  auto square = [] (int i) { return i * i; };
  mofunc = square;                      // refer to lambda
  callMO(std::move(mofunc));
  callMO(square);
}