## Smart Pointers

`virtual_ptr` can also be used in combination with smart pointers.
`virtual_ptr<std::shared_ptr<Class>>` (aliased to `shared_virtual_ptr<Class>`)
and `virtual_ptr<std::unique_ptr<Class>>` (aliased to
`unique_virtual_ptr<Class>`) deliver the convenience of automatic memory
management with the speed of `virtual_ptr`. Convenience functions
`make_shared_virtual` and `make_unique_virtual` create an object and return a
smart virtual_ptr to it. Since the exact type of the object is known, the vptr
is read from a static variable, without incuring the cost of a hash table
lookup.

Here is a variaton of the AST example that uses dynamic allocation and unique
pointers:


[source,c++]
----
include::{examplesdir}/ast_unique_ptr.cpp[tag=ast,indent=0]
----