Boost.Variant

Safe, generic, stack-based discriminated union container.

The variant class template is a safe, generic, stack-based discriminated union container, offering a simple solution for manipulating an object from a heterogeneous set of types in a uniform manner. Whereas standard containers such as std::vector may be thought of as "multi-value, single type," variant is "multi-type, single value."

Notable features of boost::variant include:

* Full value semantics, including adherence to standard overload resolution rules for conversion operations.
* Compile-time type-safe value visitation via boost::apply_visitor.
* Run-time checked explicit value retrieval via boost::get.
* Support for recursive variant types via both boost::make_recursive_variant and boost::recursive_wrapper.
* Efficient implementation -- stack-based when possible (see the section called “"Never-Empty" Guarantee” for more details).

Example from: http://stackoverflow.com/questions/607458/storing-a-list-of-arbitrary-objects-in-c