C++ Finally

finally1.cpp

#include <functional>
#include <iostream>

// https://www.youtube.com/watch?v=eG5suWcHI8M
// Lightning Talk: FINALLY - The Presentation You've All Been Waiting For - Louis Thomas - CppCon 2021

class Finally {
 public:
  std::function<void()> m_action;

  explicit Finally(std::function<void()> action)
      : m_action(std::move(action)) {}

  ~Finally() { m_action(); }
};

int main() {
  Finally test([]() { std::cout << "Done.\n"; });
  return 0;
}

finally2.cpp

#include <iostream>

template <typename ActionT>
class Finally {
 public:
  ActionT m_action;

  explicit Finally(ActionT action) : m_action(std::move(action)) {}

  ~Finally() { m_action(); }
};

int main() {
  Finally test([]() { std::cout << "Done.\n"; });
  return 0;
}

finally3.cpp

#include <iostream>

template <typename Fn>
auto Finally(Fn action) {
  class FinallyImpl {
   public:
    Fn m_action;

    explicit FinallyImpl(Fn action) : m_action(std::move(action)) {}
    ~FinallyImpl() { m_action(); }
  };
  return FinallyImpl(std::move(action));
}

int main() {
  // FILE* f = fopen(...)
  // auto close_f = Finally([&f]{ fclose(f); });
  auto test = Finally([]() { std::cout << "Done.\n"; });
  return 0;
}