libcxx/include/__cxx03/__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 <__cxx03/__config>
  13 #include <__cxx03/__pstl/backend_fwd.h>
  14 #include <__cxx03/__type_traits/conditional.h>
  15 #include <__cxx03/__type_traits/enable_if.h>
  16 #include <__cxx03/__type_traits/integral_constant.h>
  17 #include <__cxx03/__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 <__cxx03/__undef_macros>
  25
  26 _LIBCPP_BEGIN_NAMESPACE_STD
  27 namespace __pstl {
  28
  29 template <template <class, class> class _Algorithm, class _Backend, class _ExecutionPolicy, class = void>
  30 constexpr bool __is_implemented_v = false;
  31
  32 template <template <class, class> class _Algorithm, class _Backend, class _ExecutionPolicy>
  33 constexpr bool __is_implemented_v<_Algorithm,
  34                                   _Backend,
  35                                   _ExecutionPolicy,
  36                                   __enable_if_t<sizeof(_Algorithm<_Backend, _ExecutionPolicy>)>> = true;
  37
  38 // Helpful to provide better error messages. This will show the algorithm and the execution policy
  39 // in the compiler diagnostic.
  40 template <template <class, class> class _Algorithm, class _ExecutionPolicy>
  41 constexpr bool __cant_find_backend_for = false;
  42
  43 template <template <class, class> class _Algorithm, class _BackendConfiguration, class _ExecutionPolicy>
  44 struct __find_first_implemented;
  45
  46 template <template <class, class> class _Algorithm, class _ExecutionPolicy>
  47 struct __find_first_implemented<_Algorithm, __backend_configuration<>, _ExecutionPolicy> {
  48   static_assert(__cant_find_backend_for<_Algorithm, _ExecutionPolicy>,
  49                 "Could not find a PSTL backend for the given algorithm and execution policy");
  50 };
  51
  52 template <template <class, class> class _Algorithm, class _B1, class... _Bn, class _ExecutionPolicy>
  53 struct __find_first_implemented<_Algorithm, __backend_configuration<_B1, _Bn...>, _ExecutionPolicy>
  54     : _If<__is_implemented_v<_Algorithm, _B1, _ExecutionPolicy>,
  55           __type_identity<_Algorithm<_B1, _ExecutionPolicy>>,
  56           __find_first_implemented<_Algorithm, __backend_configuration<_Bn...>, _ExecutionPolicy> > {};
  57
  58 template <template <class, class> class _Algorithm, class _BackendConfiguration, class _ExecutionPolicy>
  59 using __dispatch = typename __find_first_implemented<_Algorithm, _BackendConfiguration, _ExecutionPolicy>::type;
  60
  61 } // namespace __pstl
  62 _LIBCPP_END_NAMESPACE_STD
  63
  64 _LIBCPP_POP_MACROS
  65
  66 #endif // _LIBCPP___PSTL_DISPATCH_H