Boost C++ Libraries: Ticket #6606: Map: rbtree_node doesn't use allocator_traits to construct m_data

Fri, 24 Feb 2012 03:45:19 GMT

I guess another option would be to tuck a class like this (which I just made up) into your details, somewhere:

#include <boost/type_traits.hpp>
template <typename Ty, typename Alloc>
class allocator_constructed
{
public:
   template <typename T, typename Args...>
   allocator_constructed(const Alloc &alloc, Args &&...args)
      : _alloc(alloc)
   {
      allocator_traits<Alloc>::construct(_alloc,
         static_cast<Ty*>(static_cast<void*>(&data)),
         boost::forward<Args>(args)...);
   }
   ~manually_constructed() {
      allocator_traits<Alloc>::destroy(_alloc,
         static_cast<Ty*>(static_cast<void*>(&data)));
   }
   Ty& operator*() {
      return *static_cast<Ty*>(static_cast<void*>(&data));
   }
   const Ty& operator*() const {
      return *static_cast<Ty*>(static_cast<void*>(&data));
   }
   Ty* operator->() {
      return static_cast<Ty*>(static_cast<void*>(&data));
   }
   const Ty* operator->() const {
      return static_cast<Ty*>(static_cast<void*>(&data));
   }
private:
   Alloc _alloc;
   boost::aligned_storage<sizeof(Ty), std::alignment_of<Ty>::value> data;
};

And then have members of this class.

Thu, 22 Mar 2012 19:26:08 GMT

One further note:

I was reading through the standard, and came across this (§23.2.1¶3):

For the components affected by this subclause that declare an allocator_type, objects stored in these components shall be constructed using the allocator_traits<allocator_type>::construct function and destroyed using the allocator_traits<allocator_type>::destroy function (20.6.8.2). These functions are called only for the container’s element type, not for internal types used by the container. [ Note: This means, for example, that a node-based container might need to construct nodes containing aligned buffers and call construct to place the element into the buffer. —end note ]

My understanding, then, is that while construct should be called for the pair, it should not be called for rbtree_node (which it currently is).

status changed; resolution set

Ion Gaztañaga — Fri, 24 Aug 2012 21:32:16 GMT

status new → closed
resolution → fixed

Fixed in Boost 1.50