Description

The template class describes an object that manages storage allocation and freeing for arrays of objects of non-const, non-reference, object type Ty. An object of class allocator is the default allocator object specified in the constructors for several container template classes in the Standard C++ Library.

Template class allocator supplies several type definitions that are rather pedestrian. They hardly seem worth defining. But another class with the same members might choose more interesting alternatives. Constructing a container with an allocator object of such a class gives individual control over allocation and freeing of elements controlled by that container.

For example, an allocator object might allocate storage on a private heap. Or it might allocate storage on a far heap, requiring nonstandard pointers to access the allocated objects. Or it might specify, through the type definitions it supplies, that elements be accessed through special accessor objects that manage shared memory, or perform automatic garbage collection. Hence, a class that allocates storage using an allocator object should use these types religiously for declaring pointer and reference objects (as do the containers in the Standard C++ Library).

Thus, an allocator defines the types (among others):

• pointer — behaves like a pointer to Ty
• const_pointer — behaves like a const pointer to Ty
• reference — behaves like a reference to Ty
• const_reference — behaves like a const reference to Ty

These types specify the form that pointers and references must take for allocated elements. (allocator::pointer is not necessarily the same as Ty * for all allocator objects, even though it has this obvious definition for class allocator.)