| /* |
| * |
| * Copyright 2016 gRPC authors. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| * |
| */ |
| |
| #ifndef GRPC_CORE_LIB_GPRPP_MANUAL_CONSTRUCTOR_H |
| #define GRPC_CORE_LIB_GPRPP_MANUAL_CONSTRUCTOR_H |
| |
| // manually construct a region of memory with some type |
| |
| #include <grpc/support/port_platform.h> |
| |
| #include <stddef.h> |
| #include <stdlib.h> |
| #include <new> |
| #include <type_traits> |
| #include <utility> |
| |
| #include <grpc/support/log.h> |
| |
| namespace grpc_core { |
| |
| // this contains templated helpers needed to implement the ManualConstructors |
| // in this file. |
| namespace manual_ctor_impl { |
| |
| // is_one_of returns true it a class, Member, is present in a variadic list of |
| // classes, List. |
| template <class Member, class... List> |
| class is_one_of; |
| |
| template <class Member, class... List> |
| class is_one_of<Member, Member, List...> { |
| public: |
| static constexpr const bool value = true; |
| }; |
| |
| template <class Member, class A, class... List> |
| class is_one_of<Member, A, List...> { |
| public: |
| static constexpr const bool value = is_one_of<Member, List...>::value; |
| }; |
| |
| template <class Member> |
| class is_one_of<Member> { |
| public: |
| static constexpr const bool value = false; |
| }; |
| |
| // max_size_of returns sizeof(Type) for the largest type in the variadic list |
| // of classes, Types. |
| template <class... Types> |
| class max_size_of; |
| |
| template <class A> |
| class max_size_of<A> { |
| public: |
| static constexpr const size_t value = sizeof(A); |
| }; |
| |
| template <class A, class... B> |
| class max_size_of<A, B...> { |
| public: |
| static constexpr const size_t value = sizeof(A) > max_size_of<B...>::value |
| ? sizeof(A) |
| : max_size_of<B...>::value; |
| }; |
| |
| // max_size_of returns alignof(Type) for the largest type in the variadic list |
| // of classes, Types. |
| template <class... Types> |
| class max_align_of; |
| |
| template <class A> |
| class max_align_of<A> { |
| public: |
| static constexpr const size_t value = alignof(A); |
| }; |
| |
| template <class A, class... B> |
| class max_align_of<A, B...> { |
| public: |
| static constexpr const size_t value = alignof(A) > max_align_of<B...>::value |
| ? alignof(A) |
| : max_align_of<B...>::value; |
| }; |
| |
| } // namespace manual_ctor_impl |
| |
| template <class BaseType, class... DerivedTypes> |
| class PolymorphicManualConstructor { |
| public: |
| // No constructor or destructor because one of the most useful uses of |
| // this class is as part of a union, and members of a union could not have |
| // constructors or destructors till C++11. And, anyway, the whole point of |
| // this class is to bypass constructor and destructor. |
| |
| BaseType* get() { return reinterpret_cast<BaseType*>(&space_); } |
| const BaseType* get() const { |
| return reinterpret_cast<const BaseType*>(&space_); |
| } |
| |
| BaseType* operator->() { return get(); } |
| const BaseType* operator->() const { return get(); } |
| |
| BaseType& operator*() { return *get(); } |
| const BaseType& operator*() const { return *get(); } |
| |
| template <class DerivedType> |
| void Init() { |
| FinishInit(new (&space_) DerivedType); |
| } |
| |
| // Init() constructs the Type instance using the given arguments |
| // (which are forwarded to Type's constructor). |
| // |
| // Note that Init() with no arguments performs default-initialization, |
| // not zero-initialization (i.e it behaves the same as "new Type;", not |
| // "new Type();"), so it will leave non-class types uninitialized. |
| template <class DerivedType, typename... Ts> |
| void Init(Ts&&... args) { |
| FinishInit(new (&space_) DerivedType(std::forward<Ts>(args)...)); |
| } |
| |
| // Init() that is equivalent to copy and move construction. |
| // Enables usage like this: |
| // ManualConstructor<std::vector<int>> v; |
| // v.Init({1, 2, 3}); |
| template <class DerivedType> |
| void Init(const DerivedType& x) { |
| FinishInit(new (&space_) DerivedType(x)); |
| } |
| template <class DerivedType> |
| void Init(DerivedType&& x) { |
| FinishInit(new (&space_) DerivedType(std::move(x))); |
| } |
| |
| void Destroy() { get()->~BaseType(); } |
| |
| private: |
| template <class DerivedType> |
| void FinishInit(DerivedType* p) { |
| static_assert( |
| manual_ctor_impl::is_one_of<DerivedType, DerivedTypes...>::value, |
| "DerivedType must be one of the predeclared DerivedTypes"); |
| GPR_ASSERT(static_cast<BaseType*>(p) == p); |
| } |
| |
| typename std::aligned_storage< |
| grpc_core::manual_ctor_impl::max_size_of<DerivedTypes...>::value, |
| grpc_core::manual_ctor_impl::max_align_of<DerivedTypes...>::value>::type |
| space_; |
| }; |
| |
| template <typename Type> |
| class ManualConstructor { |
| public: |
| // No constructor or destructor because one of the most useful uses of |
| // this class is as part of a union, and members of a union could not have |
| // constructors or destructors till C++11. And, anyway, the whole point of |
| // this class is to bypass constructor and destructor. |
| |
| Type* get() { return reinterpret_cast<Type*>(&space_); } |
| const Type* get() const { return reinterpret_cast<const Type*>(&space_); } |
| |
| Type* operator->() { return get(); } |
| const Type* operator->() const { return get(); } |
| |
| Type& operator*() { return *get(); } |
| const Type& operator*() const { return *get(); } |
| |
| void Init() { new (&space_) Type; } |
| |
| // Init() constructs the Type instance using the given arguments |
| // (which are forwarded to Type's constructor). |
| // |
| // Note that Init() with no arguments performs default-initialization, |
| // not zero-initialization (i.e it behaves the same as "new Type;", not |
| // "new Type();"), so it will leave non-class types uninitialized. |
| template <typename... Ts> |
| void Init(Ts&&... args) { |
| new (&space_) Type(std::forward<Ts>(args)...); |
| } |
| |
| // Init() that is equivalent to copy and move construction. |
| // Enables usage like this: |
| // ManualConstructor<std::vector<int>> v; |
| // v.Init({1, 2, 3}); |
| void Init(const Type& x) { new (&space_) Type(x); } |
| void Init(Type&& x) { new (&space_) Type(std::move(x)); } |
| |
| void Destroy() { get()->~Type(); } |
| |
| private: |
| typename std::aligned_storage<sizeof(Type), alignof(Type)>::type space_; |
| }; |
| |
| } // namespace grpc_core |
| |
| #endif |