lib/function.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 call(std::function<int(int)> f) {
  if (f) {
    std::cout << f(7) << '\n';
  }
}

int main()
{
  std::function<int(int)> func;
  call(func);

  func = cube;                          // refer to ordinary function
  call(func);

  func = std::negate<int>{};            // refer to function object
  call(func);

  func = [] (int i) { return i * i; };  // refer to lambda
  call(func);
}