CODEWITHSUNDEEP
c++oopclassinheritance
Rody Oldenhuis
Rody Oldenhuis

Reputation: 38052

Is there an interface mechanism for nested enum classes?

In C++, pure virtual functions provide the functionality of an interface. That is, any subclasses must implement all pure-virtual functions in the base class:

class myClass {
    virtual bool implementme() = 0; // MUST be implemented
};

class mySubClass : public myClass {
    bool implementme() {} // REQUIRED
};

Is there a similar mechanism for nested (enum) classes? That is, I'm looking for something like

class myClass {
    virtual enum class myEnum = 0; // MUST be implemented
};

class mySubClass : public myClass {
    enum class myEnum {}; // REQUIRED
};

Upvotes: 2

Views: 279

Answers (2)

Dark Falcon
Dark Falcon

Reputation: 44201

Since you say that the implementer is not part of your code base (thus not producing a compile error), I must assume you are writing a library, and that the code which uses this enum is in the consumer of the library.

I would recommend that you use CRTP as follows:

class myClass {
};

template<typename T> class myClassImpl : public myClass {
  static_assert(std::is_enum<typename T::myEnum>::value, "Subclasses of myClassImpl must provide the myEnum enum class");
};

class mySubClass : public myClassImpl<mySubClass> {
    enum class myEnum {};
};

Upvotes: 1

David
David

Reputation: 28178

This wouldn't make a whole lot of sense. Someone could only have visibility to only the base class (not the derived class) and get back a myEnum from the return of some virtual function, where myEnum is an incomplete type. There is no mechanism for virtual types of any kind, including enums. Do you really want a virtual table looking up your type anyway?

Upvotes: 0

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