Scoped Enumerations

Traditional C++ enumerations provide a way to create named constants. However, they come with a rather low level of type checking. Also the scope for enumeration names is the scope that encloses the enumeration definition, which means that two enumerations defined in the same scope must not have enumeration members with the same name. Finally, enumerations may not be completely portable because different implementations may choose to use different underlying types. C++11 introduces a variant of enumerations that addresses these problems. The new form is indicated by using class or struct in the definition:

enum Old1 {yes, no, maybe};                        // traditional form
enum class New1 {never, sometimes, often, always}; // new form
enum struct New2 {never, lever, sever};            // new form

The new forms avoid name conflicts by requiring explicit scoping. Thus, you would use New1::never and New2::never to identify those particular enumerations. Chapter 10, “Objects and Classes,” provides more details.