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/*
*
* 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
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