auto_space.hpp

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/* Copyright 2003-2004 Joaqu韓 M L髉ez Mu駉z.
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 *
 * See http://www.boost.org/libs/multi_index for library home page.
 */

#ifndef BOOST_MULTI_INDEX_DETAIL_AUTO_SPACE_HPP
#define BOOST_MULTI_INDEX_DETAIL_AUTO_SPACE_HPP

#include <boost/detail/allocator_utilities.hpp>
#include <boost/noncopyable.hpp>
#include <memory>

namespace boost{

namespace multi_index{

namespace detail{

/* auto_space provides uninitialized space suitably to store
 * a given number of elements of a given type.
 */

/* NB: it is not clear whether using an allocator to handle
 * zero-sized arrays of elements is conformant or not. GCC 3.3.1
 * and prior fail here, other stdlibs handle the issue gracefully.
 * To be on the safe side, the case n==0 is given special treatment.
 * References:
 *   GCC Bugzilla, "standard allocator crashes when deallocating segment
 *    "of zero length", http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14176
 *   C++ Standard Library Defect Report List (Revision 28), issue 199
 *     "What does allocate(0) return?",
 *     http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#199
 */

template<typename T,typename Allocator=std::allocator<T> >
struct auto_space:private noncopyable
{
  explicit auto_space(const Allocator& al=Allocator(),std::size_t n=1):
  al_(al),n_(n),data_(n_?al_.allocate(n_):0)
  {}

  ~auto_space()
  {
    if(n_)al_.deallocate(data_,n_);
  }

  T* data()const{return data_;}
    
private:
  typename boost::detail::allocator::rebind_to<
    Allocator,T>::type                          al_;
  std::size_t                                   n_;
  T*                                            data_;
};

} /* namespace multi_index::detail */

} /* namespace multi_index */

} /* namespace boost */

#endif