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How to define a template function that only accepts a base class with parameter T of type its subclass?

February 19, 2022

It is not specific to casting. My scenario is how to define a template function that only accepts a base class for parameter T of type subclass.

template<typename T> // T must be a subclass
T* DoSomething(<I don't know> parent) // parent must be a base class
{
    // here the specified subclass of type T is produced.
    // return object of type T which is a subclass.
}

A contrived usage:

Parent* p = new Child();
Child* c = DoSomething<Child>(p);
delete p;

>Solution :

One way could be by using std::is_base_of or std::is_base_of_v in combination with a static_assert:

template<typename Derived, typename Base>
Derived* CastChecked(Base* parent)
{
    static_assert(std::is_base_of_v<Base,Derived>);

    return dynamic_cast<Derived*>(parent);
}