我正在实现基于2018年圣迭戈草案（N4791）的向量，并在实现强异常安全性方面遇到了一些问题。
以下是一些代码：
我看到这段代码有两个问题。我尝试遵循
另一个问题在于
以下是一些代码：
template <typename T, typename Allocator>
void Vector<T, Allocator>::push_back(const T& value)
{
if (buffer_capacity == 0)
{
this->Allocate(this->GetSufficientCapacity(1));
}
if (buffer_size < buffer_capacity)
{
this->Construct(value);
return;
}
auto new_buffer = CreateNewBuffer(this->GetSufficientCapacity(
buffer_size + 1), allocator);
this->MoveAll(new_buffer);
try
{
new_buffer.Construct(value);
}
catch (...)
{
this->Rollback(new_buffer, std::end(new_buffer));
throw;
}
this->Commit(std::move(new_buffer));
}
template <typename T, typename Allocator>
void Vector<T, Allocator>::Allocate(size_type new_capacity)
{
elements = std::allocator_traits<Allocator>::allocate(allocator,
new_capacity);
buffer_capacity = new_capacity;
}
template <typename T, typename Allocator> template <typename... Args>
void Vector<T, Allocator>::Construct(Args&&... args)
{
// TODO: std::to_address
std::allocator_traits<Allocator>::construct(allocator,
elements + buffer_size, std::forward<Args>(args)...);
++buffer_size;
}
template <typename T, typename Allocator>
Vector<T, Allocator> Vector<T, Allocator>::CreateNewBuffer(
size_type new_capacity, const Allocator& new_allocator)
{
Vector new_buffer{new_allocator};
new_buffer.Allocate(new_capacity);
return new_buffer;
}
template <typename T, typename Allocator>
void Vector<T, Allocator>::Move(iterator first, iterator last, Vector& buffer)
{
if (std::is_nothrow_move_constructible_v<T> ||
!std::is_copy_constructible_v<T>)
{
std::move(first, last, std::back_inserter(buffer));
}
else
{
std::copy(first, last, std::back_inserter(buffer));
}
}
template <typename T, typename Allocator
void Vector<T, Allocator>::MoveAll(Vector& buffer)
{
Move(std::begin(*this), std::end(*this), buffer);
}
template <typename T, typename Allocator>
void Vector<T, Allocator>::Rollback(Vector& other, iterator last) noexcept
{
if (!std::is_nothrow_move_constructible_v<T> &&
std::is_copy_constructible_v<T>)
{
return;
}
std::move(std::begin(other), last, std::begin(*this));
}
template <typename T, typename Allocator>
void Vector<T, Allocator>::Commit(Vector&& other) noexcept
{
this->Deallocate();
elements = other.elements;
buffer_capacity = other.buffer_capacity;
buffer_size = other.buffer_size;
allocator = other.allocator;
other.elements = nullptr;
other.buffer_capacity = 0;
other.buffer_size = 0;
}
我看到这段代码有两个问题。我尝试遵循
std::move_if_noexcept 的逻辑，但如果元素是 nothrow 可移动构造的，但 allocator_traits::construct 在自定义分配器内部的某些日志记录代码中抛出异常怎么办？那么我的 MoveAll 调用将抛出并仅产生基本保证。这是否是标准上的缺陷？Allocator::construct 应该有更严格的措辞吗？另一个问题在于
Rollback。只有移动的元素是 nothrow 可移动可分配的，它才会真正产生强烈的保证。否则，同样只有基本保证。这是它应该的方式吗？