1 /* 2 * Copyright 2014 Google Inc. All rights reserved. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef FRUIT_META_ERRORS_H 18 #define FRUIT_META_ERRORS_H 19 20 #include <fruit/impl/meta/basics.h> 21 #include <fruit/impl/meta/logical_operations.h> 22 23 namespace fruit { 24 namespace impl { 25 namespace meta { 26 27 template <typename T> 28 struct CheckIfError { 29 using type = T; 30 }; 31 32 template <typename ErrorTag, typename... ErrorArgs> 33 struct CheckIfError<Error<ErrorTag, ErrorArgs...>> { 34 using type = typename ErrorTag::template apply<ErrorArgs...>; 35 }; 36 37 // ConstructError(ErrorTag, Args...) returns Error<ErrorTag, Args...>. 38 // Never construct an Error<...> directly, using this metafunction makes debugging easier. 39 struct ConstructError { 40 template <typename ErrorTag, typename... Args> 41 struct apply { 42 #if FRUIT_DEEP_TEMPLATE_INSTANTIATION_STACKTRACES_FOR_ERRORS 43 static_assert(true || sizeof(typename CheckIfError<Error<ErrorTag, UnwrapType<Args>...>>::type), ""); 44 #endif 45 using type = Error<ErrorTag, typename TypeUnwrapper<Args>::type...>; 46 }; 47 }; 48 49 // Extracts the first error in the given types. 50 struct ExtractFirstError { 51 template <typename... Types> 52 struct apply; 53 54 template <typename Type, typename... Types> 55 struct apply<Type, Types...> : public apply<Types...> {}; 56 57 template <typename ErrorTag, typename... ErrorParams, typename... Types> 58 struct apply<Error<ErrorTag, ErrorParams...>, Types...> { 59 using type = Error<ErrorTag, ErrorParams...>; 60 }; 61 }; 62 63 } // namespace meta 64 } // namespace impl 65 } // namespace fruit 66 67 #endif // FRUIT_META_ERRORS_H 68
