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Diffstat (limited to 'src/core/lib/gprpp/manual_constructor.h')
-rw-r--r-- | src/core/lib/gprpp/manual_constructor.h | 211 |
1 files changed, 211 insertions, 0 deletions
diff --git a/src/core/lib/gprpp/manual_constructor.h b/src/core/lib/gprpp/manual_constructor.h new file mode 100644 index 0000000000..cee38abc1b --- /dev/null +++ b/src/core/lib/gprpp/manual_constructor.h @@ -0,0 +1,211 @@ +/* + * + * 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 <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(reinterpret_cast<BaseType*>(static_cast<DerivedType*>(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 |