On Sun, Apr 7, 2024 at 9:19 PM Jens Maurer wrote:
>
> struct Base { };
> struct Derived {};

I'm guessing you meant

    struct Derived : Base {};


> int f(Base * b) { // not a template
> typeid(*b); // yields std::type_info object for "Derived"
> return 0;
> }
>
> int x = f(new Derived);


With regard to the member function std::type_info::is_polymorphic, the
best we can do is keep its behaviour consistent with how dynamic_cast
works. So for example if we have:

    struct Base1 {};
    struct Base2 { virtual ~Base2(void){} };
    struct Base3 : Base2 {};
    struct Derived : Base1, Base3 {};

    Derived var;
    Base1 * p1 = &var;
    Base2 * p2 = &var;
    Base3 * p3 = &var;

    static_assert( false == typeid(*p1).is_polymorphic() );
    static_assert( true == typeid(*p1).is_polymorphic() );
    static_assert( true == typeid(*p1).is_polymorphic() );

That is to say: is_polymorphic() will return false when invoked on the
type_info of a pointer to a non-polymorphic base class (even if the
most derived object is polymorphic).