scope_exit.h

// this code is in the public domain. see the LICENSE file for details.
// Simple implementation of Andrei Alexandrescu's scope guard, from one of his C++ talks.
#pragma once

#include <utility>

namespace detail {

template<typename Lambda> class scope_exit {
public:
    explicit scope_exit(Lambda lambda);
    scope_exit(scope_exit&& lambda);
    ~scope_exit();
    scope_exit() = delete;
    scope_exit(scope_exit const&) = delete;
    scope_exit &operator =(scope_exit const&) = delete;
private:
    Lambda lambda_;
    bool active_;
};

template<typename Lambda> scope_exit<Lambda>::scope_exit(Lambda lambda)
  : lambda_(std::move(lambda)), active_(true) {
}

template<typename Lambda> scope_exit<Lambda>::scope_exit(scope_exit&& rhs)
  : lambda_(std::move(rhs.lambda_)), active_(rhs.active_) {
  rhs.active_ = false;
}

template<typename Lambda> scope_exit<Lambda>::~scope_exit() {
  if (active_) { lambda_(); }
}

template<typename Lambda> scope_exit<Lambda> make_scope_exit(Lambda l) {
  return scope_exit<Lambda>(std::move(l));
}

enum class scope_exit_placeholder {};

template<typename Lambda>
scope_exit<Lambda> operator +(scope_exit_placeholder, Lambda&& l) {
  return make_scope_exit<Lambda>(std::forward<Lambda>(l));
}

}

#define SCOPE_EXIT_CONCAT_INNER(x, y) x##y
#define SCOPE_EXIT_CONCAT(x, y) SCOPE_EXIT_CONCAT_INNER(x, y)

#define SCOPE_EXIT \
  auto SCOPE_EXIT_CONCAT(scope_exit_, __LINE__) = ::detail::scope_exit_placeholder() + [&]()