Loki/include/loki/Allocator.h

////////////////////////////////////////////////////////////////////////////////
// The Loki Library
// Copyright (c) 2008 by Rich Sposato
//
// Permission to use, copy, modify, distribute and sell this software for any 
//     purpose is hereby granted without fee, provided that the above copyright 
//     notice appear in all copies and that both that copyright notice and this 
//     permission notice appear in supporting documentation.
// The author makes no representations about the 
//     suitability of this software for any purpose. It is provided "as is" 
//     without express or implied warranty.
////////////////////////////////////////////////////////////////////////////////

#ifndef LOKI_ALLOCATOR_HPP_INCLUDED
#define LOKI_ALLOCATOR_HPP_INCLUDED

// $Id$

// Requires project to be compiled with loki/src/SmallObj.cpp and loki/src/Singleton.cpp

#include <loki/SmallObj.h>


namespace Loki
{


//-----------------------------------------------------------------------------

/** @class LokiAllocator
 Adapts Loki's Small-Object Allocator for STL container classes.
 This class provides all the functionality required for STL allocators, but
 uses Loki's Small-Object Allocator to perform actual memory operations.
 Implementation comes from a post in Loki forums (by Rasmus Ekman?).
 */
template
<
    typename Type,
    typename AllocT = Loki::AllocatorSingleton<>
>
class LokiAllocator
{
public:

    typedef ::std::size_t size_type;
    typedef ::std::ptrdiff_t difference_type;
    typedef Type * pointer;
    typedef const Type * const_pointer;
    typedef Type & reference;
    typedef const Type & const_reference;
    typedef Type value_type;

    /// Default constructor does nothing.
    inline LokiAllocator( void ) throw() { }

    /// Copy constructor does nothing.
    inline LokiAllocator( const LokiAllocator & ) throw() { }

    /// Type converting allocator constructor does nothing.
    template < typename Type1 >
    inline LokiAllocator( const LokiAllocator< Type1 > & ) throw() { }

    /// Destructor does nothing.
    inline ~LokiAllocator() throw() { }

    /// Convert an allocator<Type> to an allocator <Type1>.
    template < typename Type1 >
    struct rebind
    {
        typedef LokiAllocator< Type1 > other;
    };

    /// Return address of reference to mutable element.
    pointer address( reference elem ) const { return &elem; }

    /// Return address of reference to const element.
    const_pointer address( const_reference elem ) const { return &elem; }

    /** Allocate an array of count elements.  Warning!  The true parameter in
     the call to Allocate means this function can throw exceptions.  This is
     better than not throwing, and returning a null pointer in case the caller
     assumes the return value is not null.
     @param count # of elements in array.
     @param hint Place where caller thinks allocation should occur.
     @return Pointer to block of memory.
     */
    pointer allocate( size_type count, const void * hint = 0 )
    {
        (void)hint;  // Ignore the hint.
        void * p = AllocT::Instance().Allocate( count * sizeof( Type ), true );
        return reinterpret_cast< pointer >( p );
    }

    /// Ask allocator to release memory at pointer with size bytes.
    void deallocate( pointer p, size_type size )
    {
        AllocT::Instance().Deallocate( p, size * sizeof( Type ) );
    }

    /// Calculate max # of elements allocator can handle.
    size_type max_size( void ) const throw()
    {
        // A good optimizer will see these calculations always produce the same
        // value and optimize this function away completely.
        const size_type max_bytes = size_type( -1 );
        const size_type bytes = max_bytes / sizeof( Type );
        return bytes;
    }

    /// Construct an element at the pointer.
    void construct( pointer p, const Type & value )
    {
        // A call to global placement new forces a call to copy constructor.
        ::new( p ) Type( value );
    }

    /// Destruct the object at pointer.
    void destroy( pointer p )
    {
        // If the Type has no destructor, then some compilers complain about
        // an unreferenced parameter, so use the void cast trick to prevent
        // spurious warnings.
        (void)p;
        p->~Type();
    }

};

//-----------------------------------------------------------------------------

/** All equality operators return true since LokiAllocator is basically a
 monostate design pattern, so all instances of it are identical.
 */
template < typename Type >
inline bool operator == ( const LokiAllocator< Type > &, const LokiAllocator< Type > & )
{
    return true;
}

/** All inequality operators return false since LokiAllocator is basically a
 monostate design pattern, so all instances of it are identical.
 */
template < typename Type >
inline bool operator != ( const LokiAllocator< Type > & , const LokiAllocator< Type > & )
{
    return false;
}

//-----------------------------------------------------------------------------

} // namespace Loki

#endif // LOKI_ALLOCATOR_INCLUDED