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 "coord.hpp"
template<typename T>
concept GeoObj = requires(T x) {
{ x.draw() } -> void;
{ x.center_of_gravity() } -> Coord;
//...
};