CODEWITHSUNDEEP
c++oopc++11enumsclass-design
squall_coder
squall_coder

Reputation: 59

Propagate an enum class to a higher level class

This is a fairly basic problem but I'd like some input on what the best practice is. My issue is how do you propagate an enum from a sub-class to a higher level class so that it is visible to the main class's caller?

For example, say I have a class Bike. Bike will initialize sub-classes Wheel, Frame, Chain, etc. that make up a bike. Frame might have an enum such as FrameColor, Chain might have an enum such as LinkType, etc. Now let's say some higher level code wants to construct a Bike class. The constructor of Bike would require the caller to specify the LinkType, FrameColor, etc. I'd like to avoid putting the enum definitions inside a global header file, since this is bad C++ style.

Two possible approaches I've thought of but there must be a simpler, cleaner way:

Upvotes: 2

Views: 158

Answers (1)

Barry
Barry

Reputation: 304122

Why do you need to propagate anything? As like as your subobjects have their enumerations clear, you can just use them directly. Once you have Frame::Color, you don't need to make a Bike::Frame::Color... the one is sufficient. For example:

struct Frame {
    enum class Color {
        BLACK, RED
    };

    Color c;
};

struct Bike {
    Bike(Frame::Color c /*, Chain::LinkType lt, ..., */)
        : frame{c}
    { }

    Frame frame;
};

int main() {
    Bike b{Frame::Color::RED};
}

Now, if Frame is nested inside of Bike, you can just alias the enum:

struct Bike {
    struct Frame {
        enum class Color { ... };
    };

    using FrameColor = Frame::Color;
};

Bike b{Bike::FrameColor::RED};

Upvotes: 4

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