structurally you can do something similar by adding some tag (in the form of a constant or nested type) to your class. For example: template<class T> concept

structurally you can do something similar by adding some tag (in the form of a constant or nested type) to your class. For example: template<class T> concept serializable = requires { typename T::is_serializable_tag; }; void serialize(serializable auto x) {...}; struct NotSerializableClass { ... }; struct SerializableClass { using is_serializable_tag = void; ... }; serialize(NotSerializableClass{}); // error serialize(SerializableClass{}); // all good In C++, specializing a trait is also an option. So, while nominal and structural interfaces are not the same, sometimes the lines are blurred.