id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
1996,"""void"" template specialisation for the pool allocators",Armin Felke,Chris Newbold,"It might be reasonable to add a template specialisation for the allocator classes ""pool_allocator<T,..>"" and ""fast_pool_allocator<T,..>"" with T=void?

The library boost::multi_index, e.g., currently (version 1.35.0) uses the allocator<void> notation in its generic code (expecting a ""default allocator"").

In section 20.4.1 [lib.default.allocator] of the C++ standard the following specialisation is defined for class std::allocator as follows:

<code>
template <class T> class allocator;
//  specialize for  void:
template <> class allocator<void> {
public:
   typedef void*        pointer;
   typedef const void*  const_pointer;
   // reference-to-void members are impossible.
   typedef void  value_type;
   template <class U> struct rebind { typedef allocator<U> other; };
};
</code>

In order to use the pool allocators with multi_index_container and ease generic programming, I would suggest the following additions to pool_alloc.hpp:

<code>
   template<
     typename UserAllocator,
     typename Mutex,
     unsigned NextSize>
   class pool_allocator<void, UserAllocator, Mutex, NextSize> {
   public:
     typedef void*       pointer;
     typedef const void* const_pointer;
     typedef void        value_type;
     template <class U> struct rebind {
         typedef pool_allocator<U, UserAllocator, Mutex, NextSize> other;
     };
   };

   template<
     typename UserAllocator,
     typename Mutex,
     unsigned NextSize>
   class fast_pool_allocator<void, UserAllocator, Mutex, NextSize> {
   public:
     typedef void*       pointer;
     typedef const void* const_pointer;
     typedef void        value_type;
     template <class U> struct rebind {
         typedef fast_pool_allocator<U, UserAllocator, Mutex, NextSize> other;
     };
   };
</code>

Best regards
Armin Felke
",Patches,closed,Boost 1.37.0,pool,Boost 1.35.0,Optimization,fixed,,