--- /dev/null
+/*
+ *
+ * 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
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