[Boost-bugs] [Boost C++ Libraries] #1996: "void" template specialisation for the pool allocators

Subject: [Boost-bugs] [Boost C++ Libraries] #1996: "void" template specialisation for the pool allocators
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2008-06-07 16:24:04

#1996: "void" template specialisation for the pool allocators
--------------------------+-------------------------------------------------
 Reporter:  Armin Felke   |       Owner:  no-maintainer
     Type:  Patches       |      Status:  new          
Milestone:  Boost 1.35.1  |   Component:  pool         
  Version:  Boost 1.35.0  |    Severity:  Optimization 
 Keywords:                |  
--------------------------+-------------------------------------------------
 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

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/1996>
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