Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::container::erased_type
// In header: <boost/container/uses_allocator_fwd.hpp> struct erased_type { };
The erased_type struct is an empty struct that serves as a placeholder for a type T in situations where the actual type T is determined at runtime. For example, the nested type, allocator_type, is an alias for erased_type in classes that use type-erased allocators.