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
#include <utility>
template<typename T1, typename T2,
typename RT = std::decay_t<decltype(true ? std::declval<T1>()
: std::declval<T2>())>>
RT max (T1 a, T2 b)
{
return b < a ? a : b;
}