copton.net

Because the scope operator makes no difference between classes and namespaces people tend to think, that classes are like namespaces. But this is not true, as

• classes can not nest further namespaces, only further classes
• classes can not be imported by a using decleration
• classes can not be reopenend
• classes have access rights

One of the consequences is, that the "nest the enum into a namespace in order to import all constants"-trick and the "replace all enums by namespaces with constant integers"-workaround from my previous post do not work, if the enum is defined inside a class.

Enums are annoying.

• they can not be extended, e.g. by inheritance
• they can not be enriched with construtors and cast operators
• they do not introduce a new namespace

The last point is the most annoying one for me. The defined constants are embedded in the namespace which surrounds the enum. So, for instance

enum Operation1 {
    //...
    ERROR
};

enum Operation2 {
    //..
    ERROR
};

does not compile, because the two ERROR constants collide.

The same goes for a enum constant and a namespace:

namespace Plugin {
    enum Id {
        SomePlugin
    };
    // ...
    namespace SomePlugin { 
        // implementation of SomePlugin
    }
}

and similar constelations.

Another consequence is, that it is not possible to import all constants of an enum with one using statement. Instead you need somethine like this

namespace MyEnum {
    enum MyEnum {
        // constants...
    };
}

to be able to import the constants with a single using MyEnum.

Replacing a enum by a namespace with constants has some disadvantages:

• You need to enumerate the constants on your own.
• A enum function parameter must be replaced by a const int, and one can not contrain the legal values on constants from the namespace.
• You loose the convenient compiler warnings on enums, for instance if you forget a possiblity in a switch statement without a default case.

So, nothing helps. Enums are a C heritage, so no wonder that it sucks. But you nevertheless need them. *shrug*