260.md

• Did you know that C++23 added std::move_only_function?

  • https://wg21.link/P0288

#include <functional>

int main() {
  {
  std::function<int()> f{[]{return 42; }};
  auto copy = f; // okay
  auto value = f();
  }

  {
  std::move_only_function<int()> f{[] {return 42; }};
  auto copy = f; // error, call to deleted copy constructor
  auto value = f(); // undefined behaviour, dandling reference
  }
}

https://godbolt.org/z/KWTx4nd3n

• Can you comment out and fill ??? with appropirate function type (std::function or std::move_only_function) when applicable?

int main() {
  {
    auto f = [] { return 42; };
    // TODO
    // ??? f1 = f;
    // ??? f2 = std::move(f);
  }

  {
    auto value = 42;
    auto f = [v = std::move(value)] { return v; };
    // TODO
    // ??? f1 = f;
    // ??? f2 = std::move(f);
  }

  {
    auto f = [u = std::make_unique<int>(42)] { return *u; };
    // TODO
    // ??? f1 = f;
    // ??? f2 = std::move(f);
  }
}

https://godbolt.org/z/hK4EGvd1q