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_LAMBDA_INVOKER_H 18 #define FRUIT_LAMBDA_INVOKER_H 19 20 #include <fruit/impl/fruit-config.h> 21 #include <fruit/impl/injection_errors.h> 22 #include <fruit/impl/meta/errors.h> 23 #include <fruit/impl/meta/metaprogramming.h> 24 #include <fruit/impl/meta/signatures.h> 25 #include <fruit/impl/meta/wrappers.h> 26 27 #include <cstddef> 28 #include <functional> 29 #include <type_traits> 30 31 namespace fruit { 32 namespace impl { 33 34 template <typename T> 35 struct SafeAlignmentOf { 36 constexpr static const std::size_t value = alignof(T); 37 }; 38 39 template <typename T, typename... Args> 40 struct SafeAlignmentOf<T(Args...)> { 41 constexpr static const std::size_t value = alignof(int); 42 }; 43 44 class LambdaInvoker { 45 public: 46 template <typename F, typename... Args> 47 FRUIT_ALWAYS_INLINE static auto invoke(Args&&... args) 48 -> decltype(std::declval<const F&>()(std::declval<Args>()...)) { 49 // We reinterpret-cast a char[] to avoid de-referencing nullptr, which would technically be 50 // undefined behavior (even though we would not access any data there anyway). 51 // Sharing this buffer for different types F would also be undefined behavior since we'd break 52 // strict aliasing between those types. 53 alignas(SafeAlignmentOf<F>::value) static char buf[1]; 54 55 FruitStaticAssert(fruit::impl::meta::IsEmpty(fruit::impl::meta::Type<F>)); 56 FruitStaticAssert(fruit::impl::meta::IsTriviallyCopyable(fruit::impl::meta::Type<F>)); 57 // Since `F' is empty, a valid value of type F is already stored at the beginning of buf. 58 F* f = reinterpret_cast<F*>((char*)buf); 59 return (*f)(std::forward<Args>(args)...); 60 } 61 }; 62 63 } // namespace impl 64 } // namespace fruit 65 66 #endif // FRUIT_LAMBDA_INVOKER_H 67