The Clonable concept

Refinement of

• Copy Constructible
• Heap Allocable
• Heap Deallocable

The Clonable concept is introduced to formalize the requirements for copying heap-allocated objects. A type T might be Clonable even though it is not Assignable or Copy Constructible. Notice that many operations on the containers does not even require the stored type to be Clonable.

Notation

Valid expressions

namespace boost
{
    template< class T >
    inline T* new_clone( const T& t )
    {
        return new T( t );
    }

    template< class T >
    void delete_clone( const T* t )
    {
        checked_delete( r );
    }
}

The Clone Allocator concept

The Clone Allocator concept is introduced to formalize the way pointer containers controls memory of the stored objects (and not the pointers to the stored objects). The clone allocator allows users to apply custom allocators/deallocators for the cloned objects.

More information can be found below:

namespace boost
{        
    struct heap_clone_allocator
    {
        template< class U >
        static U* allocate_clone( const U& r )
        {
            return new_clone( r );
        }

        template< class U >
        static void deallocate_clone( const U* r ) const
        {
            delete_clone( r );
        }
    };
}

namespace boost
{
    struct view_clone_allocator
    {
        template< class U >
        static U* allocate_clone( const U& r )
        {
            return const_cast<U*>(&r);
        }

        template< class U >
        static void deallocate_clone( const U* )
        {
            // empty
        }
    };
}

Pointer container adapters

The pointer container adapters are used when you want to make a pointer container starting from your own "normal" container. For example, you might have a map class that is extends std::map in some way; the adapter class then allows you to use your map class as a basis for a new pointer container.

The library provides an adapter for each type of standard container:

• ptr_sequence_adapter
• ptr_set_adapter
• ptr_multiset_adapter
• ptr_map_adapter
• ptr_multimap_adapter

Pointer containers

The pointer containers of this library are all built using the pointer container adapters. There is a pointer container for each type of "normal" standard container:

Map iterator operations

The map iterators are a bit different compared to the normal ones. The reason is that it is a bit clumsy to access the key and the mapped object through i->first and i->second, and one tends to forget what is what. Moreover, and more importantly, we also want to hide the pointer as much as possibble. The new style can be illustrated with a small example:

typedef ptr_map<string,int> map_t;
map_t  m;
m[ "foo" ] = 4; // insert pair
m[ "bar" ] = 5; // ditto
...
for( map_t::iterator i = m.begin(); i != m.end(); ++i )
{
         *i += 42; // add 42 to each value
         cout << "value=" << *i << ", key=" << i.key() << "n";
} 

So the difference from the normal map iterator is that

• operator*() returns a reference to the mapped object (normally it returns a reference to a std::pair, and
• that the key can be accessed through the key() function.

Class nullable

The purpose of the class is simply to tell the containers that null values should be allowed. Its definition is trivial:

namespace boost
{
    template< class T >
    struct nullable
    {
        typedef T type;
    };  
}

Please notice that nullable has no effect on the containers interface (except for is_null() functions). For example, it does not make sense to do

boost::ptr_vector< boost::nullable<T> > vec;
vec.push_back( new boost::nullable<T> ); // no no
boost::nullable<T>& ref = vec[0];        // also no no

Exception classes

There are three exceptions that are thrown by this library. The exception hierarchy looks as follows:

namespace boost
{
    class bad_ptr_container_operation : public std::exception
    {
    public:
        bad_ptr_container_operation( const char* what );
    };
    
    class bad_index : public bad_ptr_container_operation
    {
    public:
        bad_index( const char* what );
    };

    class bad_pointer : public bad_ptr_container_operation
    {
    public:
        bad_pointer();
        bad_pointer( const char* what );
    };
}

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