Examples

Example 1: auto_ptr. Objects of auto_ptr<T> are not value-like because of their transfer-of-ownership copy semantics. Using a container of auto_ptrs (e.g., a vector< auto_ptr<int> >) should fail to compile. Even if it does compile, never write that; if you want to write it, you almost certainly want a container of shared_ptrs instead.

Example 2: Heterogeneous containers. To have a container store and own objects of different but related types, such as types derived from a common Base class, prefer container< shared_ptr<Base> >. An alternative is to store proxy objects whose nonvirtual functions pass through to corresponding virtual functions of the actual object.

Example 3: Containers of non-value types. To contain objects even though they are not copyable or otherwise not value-like (e.g., DatabaseLocks and TcpConnections), prefer containing them indirectly via smart pointers (e.g., container< shared_ptr\zwbo<DatabaseLock> > and container< shared_ptr\zwbo<TcpConnection> >).

Example 4: Optional values. When you want a map<Thing, Widget>, but some Things have no associated Widget, prefer map<Thing, shared_ptr<Widget> >.

Example 5: Index containers. To have a main container hold the objects and access them using different sort orders without resorting the main container, you can set up secondary containers that "point into" the main one and sort the secondary containers in different ways using dereferenced compare predicates. But prefer a container of MainContainer::iterators (which are value-like) instead of a container of pointers.