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c++c++11crtpstatic-assert

How to secure CRTP against providing wrong superclass?

In the curiously recurring template pattern, we write

template <class Derived>
class Base {
};

class Derived : public Base<Derived> {
};

What would be a good way to make the code robust another copy-paste omissions, so that the following snippet throws a compile-time error:

class AnotherDerived : public Base<Derived> {
};

I'm using Visual C++ 2013.

Solution

  • Make Base's destructor private, and then make Derived a friend of Base<Derived>:

    template <class Derived>
class Base {
    private: ~Base() = default;
    friend Derived;
};

class Derived : public Base<Derived> {
};

    This does not actually make doing

    class AnotherDerived : public Base<Derived> {
};

    illegal, but any attempt to actually construct an AnotherDerived will fail.