Question

I’ve a basic template class, but I’d like to restrain the type of the specialisation to a set of classes or types. e.g.:

template <typename T>
class MyClass
{
.../...
private:
    T* _p;
};

MyClass<std::string> a; // OK
MYCLass<short> b;       // OK
MyClass<double> c;      // not OK

Those are just examples, the allowed types may vary.

Is that even possible? If it is, how to do so?

Thanks.

Answer 1

Another version is to leave it undefined for the forbidden types

template<typename T>
struct Allowed; // undefined for bad types!

template<> struct Allowed<std::string> { };
template<> struct Allowed<short> { };

template<typename T>
struct MyClass : private Allowed<T> { 
  // ...
};

MyClass<double> m; // nono