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 T1, typename T2>
auto max (T1 a, T2 b) -> decltype(b<a?a:b)
{
return b < a ? a : b;
}