is it possible to write a partial template specialization that is used only for class types that, for example, inherit from a specific class or comply with some other constraint that can be expressed via type traits? i.e., something like this:
class A{}
class B : public A{}
template<typename T>
class X{
int foo(){ return 4; }
};
//Insert some magic that allows this partial specialization
//only for classes which are a subtype of A
template<typename T>
class X<T>{
int foo(){ return 5; }
};
int main(){
X<int> x;
x.foo(); //Returns 4
X<A> y;
y.foo(); //Returns 5
X<B> z;
z.foo(); //Returns 5
X<A*> x2;
x2.foo(); //Returns 4
}
Usually if you want conditional partial template specialization, you'll need to provide an extra parameter, and then use enable_if:
template<typename T, typename=void>
class X {
public:
int foo(){ return 4; }
};
template<typename T>
class X<T, std::enable_if_t<std::is_base_of_v<A, T>>> {
public:
int foo(){ return 5; }
};
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