libcxx/include/__pstl/dispatch.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___PSTL_DISPATCH_H
  10 #define _LIBCPP___PSTL_DISPATCH_H
  11
  12 #include <__config>
  13 #include <__pstl/backend_fwd.h>
  14 #include <__type_traits/conditional.h>
  15 #include <__type_traits/enable_if.h>
  16 #include <__type_traits/integral_constant.h>
  17 #include <__type_traits/type_identity.h>
  18
  19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  20 #  pragma GCC system_header
  21 #endif
  22
  23 _LIBCPP_PUSH_MACROS
  24 #include <__undef_macros>
  25
  26 #if _LIBCPP_STD_VER >= 17
  27
  28 _LIBCPP_BEGIN_NAMESPACE_STD
  29 namespace __pstl {
  30
  31 template <template <class, class> class _Algorithm, class _Backend, class _ExecutionPolicy, class = void>
  32 constexpr bool __is_implemented_v = false;
  33
  34 template <template <class, class> class _Algorithm, class _Backend, class _ExecutionPolicy>
  35 constexpr bool __is_implemented_v<_Algorithm,
  36                                   _Backend,
  37                                   _ExecutionPolicy,
  38                                   __enable_if_t<sizeof(_Algorithm<_Backend, _ExecutionPolicy>)>> = true;
  39
  40 // Helpful to provide better error messages. This will show the algorithm and the execution policy
  41 // in the compiler diagnostic.
  42 template <template <class, class> class _Algorithm, class _ExecutionPolicy>
  43 constexpr bool __cant_find_backend_for = false;
  44
  45 template <template <class, class> class _Algorithm, class _BackendConfiguration, class _ExecutionPolicy>
  46 struct __find_first_implemented;
  47
  48 template <template <class, class> class _Algorithm, class _ExecutionPolicy>
  49 struct __find_first_implemented<_Algorithm, __backend_configuration<>, _ExecutionPolicy> {
  50   static_assert(__cant_find_backend_for<_Algorithm, _ExecutionPolicy>,
  51                 "Could not find a PSTL backend for the given algorithm and execution policy");
  52 };
  53
  54 template <template <class, class> class _Algorithm, class _B1, class... _Bn, class _ExecutionPolicy>
  55 struct __find_first_implemented<_Algorithm, __backend_configuration<_B1, _Bn...>, _ExecutionPolicy>
  56     : _If<__is_implemented_v<_Algorithm, _B1, _ExecutionPolicy>,
  57           __type_identity<_Algorithm<_B1, _ExecutionPolicy>>,
  58           __find_first_implemented<_Algorithm, __backend_configuration<_Bn...>, _ExecutionPolicy> > {};
  59
  60 template <template <class, class> class _Algorithm, class _BackendConfiguration, class _ExecutionPolicy>
  61 using __dispatch = typename __find_first_implemented<_Algorithm, _BackendConfiguration, _ExecutionPolicy>::type;
  62
  63 } // namespace __pstl
  64 _LIBCPP_END_NAMESPACE_STD
  65
  66 #endif // _LIBCPP_STD_VER >= 17
  67
  68 _LIBCPP_POP_MACROS
  69
  70 #endif // _LIBCPP___PSTL_DISPATCH_H