[pool] allocators missing "void" specialisation?
Hello, excuse me, I am not sure whether this hasn't already been discussed or noted elsewhere, but aren't the allocator classes "pool_allocator<T,..>" and "fast_pool_allocator<T,..>" missing a template specialisation for T=void? In section 20.4.1 [lib.default.allocator] of the C++ standard 1998 the following specialisation is defined for class std::allocator: <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> The library boost::multi_index, e.g., currently uses the std::allocator<void> notation. In order to use the pool allocators with multi_index_container I would suggest the following additions (or something similar) 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
Armin escribió:
Hello,
excuse me, I am not sure whether this hasn't already been discussed or noted elsewhere, but aren't the allocator classes "pool_allocator<T,..>" and "fast_pool_allocator<T,..>" missing a template specialisation for T=void?
In section 20.4.1 [lib.default.allocator] of the C++ standard 1998 the following specialisation is defined for class std::allocator:
<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>
The library boost::multi_index, e.g., currently uses the std::allocator<void> notation.
In order to use the pool allocators with multi_index_container I would suggest the following additions (or something similar) to pool_alloc.hpp:
[...] Hello Armin, The issue you describe was discussed some weeks ago, precisely in connection with the use of allocator<void> in Boost.MultiIndex: http://lists.boost.org/Archives/boost/2008/04/135444.php I was studying this with the intention to file a bug report against Boost.Pool, but after rereading the standard and doing some consults in the newsgroups, it's not clear to me whether this can be labeled as a genuine bug: even though std::allocator is properly specialized for void, allocator requirements do not explicitly indicate that this must also be the case for other conformant allocators. Consequently, I changed the internals of Boost.MultiIndex so as not produce allocator<void> instantiations, this will go in Boost 1.36. Nevertheless, I think your proposed change can be submitted as an enhancement request. Maybe you could file it as so in the Trac system? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo
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