src/cpp-common/vendor/wise-enum/optional.h

   1 #pragma once
   2
   3 #include "optional_common.h"
   4
   5 #include <stdexcept>
   6 #include <type_traits>
   7
   8 #if __cplusplus == 201103
   9 #define WISE_ENUM_CONSTEXPR_14
  10 #else
  11 #define WISE_ENUM_CONSTEXPR_14 constexpr
  12 #endif
  13
  14 namespace wise_enum {
  15
  16 /* A simple, *forward* compatible optional implementation. That is, it does not
  17  * provide the full std::optional interface, but all the interface it does
  18  * provide is found on std::optional, so it should not be a breaking change to
  19  * upgrade to std::optional.
  20  */
  21 template <class T>
  22 class optional {
  23 public:
  24   static_assert(std::is_enum<T>::value,
  25                 "wise enum optional is only for enum types");
  26   optional() = default;
  27   optional(T t) : m_t(t), m_active(true) {}
  28
  29   WISE_ENUM_CONSTEXPR_14 T &operator*() & { return m_t; }
  30   constexpr const T &operator*() const & { return m_t; }
  31   WISE_ENUM_CONSTEXPR_14 T &&operator*() && { return m_t; }
  32   constexpr const T &&operator*() const && { return m_t; }
  33
  34   constexpr explicit operator bool() const noexcept { return m_active; }
  35   constexpr bool has_value() const noexcept { return m_active; }
  36
  37   WISE_ENUM_CONSTEXPR_14 T &value() & {
  38     if (m_active)
  39       return m_t;
  40     else
  41       WISE_ENUM_OPTIONAL_BAD_ACCESS;
  42   }
  43   WISE_ENUM_CONSTEXPR_14 const T &value() const & {
  44     if (m_active)
  45       return m_t;
  46     else
  47       WISE_ENUM_OPTIONAL_BAD_ACCESS;
  48   }
  49
  50   WISE_ENUM_CONSTEXPR_14 T &&value() && {
  51     if (m_active)
  52       return m_t;
  53     else
  54       WISE_ENUM_OPTIONAL_BAD_ACCESS;
  55   }
  56   WISE_ENUM_CONSTEXPR_14 const T &&value() const && {
  57     if (m_active)
  58       return m_t;
  59     else
  60       WISE_ENUM_OPTIONAL_BAD_ACCESS;
  61   }
  62
  63   template <class U>
  64   WISE_ENUM_CONSTEXPR_14 T value_or(U &&u) {
  65     if (m_active)
  66       return m_t;
  67     else
  68       return std::forward<U>(u);
  69   }
  70
  71   void reset() noexcept { m_active = false; }
  72
  73   optional(const optional &other) = default;
  74   optional(optional &&other) = default;
  75   optional &operator=(const optional &other) = default;
  76   optional &operator=(optional &&other) = default;
  77
  78 private:
  79   T m_t;
  80   bool m_active = false;
  81 };
  82 } // namespace wise_enum