The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017
template<typename T>
struct IsLValueReferenceT : std::false_type { // by default no lvalue reference
};
template<typename T>
struct IsLValueReferenceT<T&> : std::true_type { // unless T is lvalue references
using BaseT = T; // type referring to
};