scopeexit.hpp

#ifndef GNR_SCOPEEXIT_HPP
# define GNR_SCOPEEXIT_HPP
# pragma once

#include <utility>

/* This counts the number of args */
#define NARGS_SEQ(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, N, ...) N
#define NARGS(...) NARGS_SEQ(__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

/* This will let macros expand before concating them */
#ifndef PRIMITIVE_CAT
# define PRIMITIVE_CAT(x, y) x ## y
#endif // PRIMITIVE_CAT

#ifndef CAT
# define CAT(x, y) PRIMITIVE_CAT(x, y)
#endif // CAT

/* This will pop the last argument off */
#define POP_LAST(...) CAT(POP_LAST_, NARGS(__VA_ARGS__))(__VA_ARGS__)
#define POP_LAST_1(x1)
#define POP_LAST_2(x1, x2) x1
#define POP_LAST_3(x1, x2, x3) x1, x2
#define POP_LAST_4(x1, x2, x3, x4) x1, x2, x3
#define POP_LAST_5(x1, x2, x3, x4, x5) x1, x2, x3, x4
#define POP_LAST_6(x1, x2, x3, x4, x5, x6) x1, x2, x3, x4, x5
#define POP_LAST_7(x1, x2, x3, x4, x5, x6, x7) x1, x2, x3, x4, x5, x6
#define POP_LAST_8(x1, x2, x3, x4, x5, x6, x7, x8) x1, x2, x3, x4, x5, x6, x7
#define POP_LAST_9(x1, x2, x3, x4, x5, x6, x7, x8, x9) x1, x2, x3, x4, x5, x6, x7, x8
#define POP_LAST_10(x1, x2, x3, x4, x5, x6, x7, x8, x9, x10) x1, x2, x3, x4, x5, x6, x7, x8, x9

/* This will return the last argument */
#define LAST(...) CAT(LAST_, NARGS(__VA_ARGS__))(__VA_ARGS__)
#define LAST_1(x1) x1
#define LAST_2(x1, x2) x2
#define LAST_3(x1, x2, x3) x3
#define LAST_4(x1, x2, x3, x4) x4
#define LAST_5(x1, x2, x3, x4, x5) x5
#define LAST_6(x1, x2, x3, x4, x5, x6) x6
#define LAST_7(x1, x2, x3, x4, x5, x6, x7) x7
#define LAST_8(x1, x2, x3, x4, x5, x6, x7, x8) x8
#define LAST_9(x1, x2, x3, x4, x5, x6, x7, x8, x9) x9
#define LAST_10(x1, x2, x3, x4, x5, x6, x7, x8, x9, x10) x10

namespace
{

template <typename T>
class scope_exit
{
  T f_;

public:
  explicit scope_exit(T&& f) noexcept : f_(std::forward<T>(f))
  {
    static_assert(noexcept(f_()), "throwing functors are unsupported");
  }

  ~scope_exit() noexcept { f_(); }
};

class scope_exit_helper { };

template<typename T>
inline scope_exit<T> make_scope_exit(T&& f) noexcept
{
  return scope_exit<T>(std::forward<T>(f));
}

template<typename T>
inline scope_exit<T> operator+(scope_exit_helper&&, T&& f) noexcept
{
  return scope_exit<T>(std::forward<T>(f));
}

}

#define SCOPE_EXIT(...) auto const CAT(scope_exit_, __LINE__)    \
  (make_scope_exit([POP_LAST(__VA_ARGS__)]() noexcept   \
    { LAST(__VA_ARGS__); }))
#define SCOPE_EXIT_ auto const CAT(scope_exit_, __LINE__) =      \
  scope_exit_helper()+[&]() noexcept
#define SCOPE_EXIT__(...) auto const CAT(scope_exit_, __LINE__) =\
  scope_exit_helper()+[__VA_ARGS__]() noexcept

#endif // GNR_SCOPEEXIT_HPP