Line data    Source code

       1           0 : // Distributed under the MIT License.
       2             : // See LICENSE.txt for details.
       3             : 
       4             : #pragma once
       5             : 
       6             : #include <type_traits>
       7             : 
       8             : /*!
       9             :  * \ingroup TypeTraitsGroup
      10             :  * \brief Generate a metafunction that will retrieve the specified
      11             :  * `static constexpr` member variable, or, if not present, a default.
      12             :  *
      13             :  * \warning Please use defaults responsibly.  In many cases it is
      14             :  * better to require the static member variable is present so the
      15             :  * functionality isn't hidden.  Also make sure to document the
      16             :  * compile-time interface, e.g. with a \ref protocols "protocol".
      17             :  */
      18           1 : #define CREATE_GET_STATIC_MEMBER_VARIABLE_OR_DEFAULT(VARIABLE_NAME)          \
      19             :   template <typename CheckingType, auto Default, typename = std::void_t<>>   \
      20             :   struct get_##VARIABLE_NAME##_or_default {                                  \
      21             :     static constexpr auto value = Default;                                   \
      22             :   };                                                                         \
      23             :   template <typename CheckingType, auto Default>                             \
      24             :   struct get_##VARIABLE_NAME##_or_default<                                   \
      25             :       CheckingType, Default,                                                 \
      26             :       std::void_t<decltype(CheckingType::VARIABLE_NAME)>> {                  \
      27             :     static_assert(                                                           \
      28             :         std::is_same_v<std::decay_t<decltype(Default)>,                      \
      29             :                        std::decay_t<decltype(CheckingType::VARIABLE_NAME)>>, \
      30             :         "Types of default and found value are not the same.");               \
      31             :     static constexpr auto value = CheckingType::VARIABLE_NAME;               \
      32             :   };                                                                         \
      33             :   template <typename CheckingType, auto Default>                             \
      34             :   constexpr auto get_##VARIABLE_NAME##_or_default_v =                        \
      35             :       get_##VARIABLE_NAME##_or_default<CheckingType, Default>::value;