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 type alias,
      11             :  * or if not present, assign a default type.
      12             :  *
      13             :  * \warning Please use defaults responsibly.  In many cases it is
      14             :  * better to require the type alias 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_TYPE_ALIAS_OR_DEFAULT(ALIAS_NAME)                           \
      19             :   template <typename CheckingType, typename Default, typename = std::void_t<>> \
      20             :   struct get_##ALIAS_NAME##_or_default {                                       \
      21             :     using type = Default;                                                      \
      22             :   };                                                                           \
      23             :   template <typename CheckingType, typename Default>                           \
      24             :   struct get_##ALIAS_NAME##_or_default<                                        \
      25             :       CheckingType, Default, std::void_t<typename CheckingType::ALIAS_NAME>> { \
      26             :     using type = typename CheckingType::ALIAS_NAME;                            \
      27             :   };                                                                           \
      28             :   template <typename CheckingType, typename Default>                           \
      29             :   using get_##ALIAS_NAME##_or_default_t =                                      \
      30             :       typename get_##ALIAS_NAME##_or_default<CheckingType, Default>::type;