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

Struct template unwrap_reference

boost::unwrap_reference — Find the type in a reference_wrapper.

// In header: <boost/core/ref.hpp>

template<typename T> 
struct unwrap_reference {
  // types
  typedef T type;
};

The typedef type is T::type if T is a reference_wrapper, T otherwise.