On Wed, 26 Apr 2023, 18:21 U.Mutlu, <um@xxxxxxxxxxx> wrote:
> Hi,
> I have a base class Base_t and multiple derived classes from it (like
> Dog_t
> and Cat_t, and so on).
> I collect the base addresses of these objects in a vector.
> By using this vector I then need to access the original objects.
> Not just some virtual functions of the objects, but the complete original
> object.
> How best to do this?
>
> The following solution is IMO not that satisfactory.
>
> Is there a better way, maybe in newer C++ standards like c++20? Something
> like:
> auto& X = helper(pBase); // X will be of type Dog_t or Cat_t etc.
>
How can helper return different types?
You could make it return std::variant<Cat*, Dog*> and then use std::visit
to access the active pointer stored in it.
So something like your Identity function that returns a variant, then do:
std::visit([](auto* x){ x->print(); }, Identity(p);
> Thx
>
>
> class Base_t { ...
> class Dog_t : public Base_t { ...
> class Cat_t : public Base_t { ...
> ...
>
> enum Type_t { Unknown, Base, Dog, Cat };
>
> struct Identity_t
> {
> Type_t Type;
> union
> {
> Base_t* pBase;
> Dog_t* pDog;
> Cat_t* pCat;
> };
>
> Identity_t() : Type(Unknown) { pBase = nullptr; }
> };
>
> Identity_t Identity(Base_t* pBase)
> {
> Identity_t I;
> if ((I.pDog = dynamic_cast<Dog_t*>(pBase))) { I.Type = Dog; return I;
> }
> if ((I.pCat = dynamic_cast<Cat_t*>(pBase))) { I.Type = Cat; return I;
> }
> return I;
> }
>
>
> // And using it like this:
> // p is the address of a derived object, ie. Dog_t* or Cat_t*
>
> auto I = Identity(p);
> if (I.Type == Dog)
> { // use I.pDog to access it
> auto& X = *I.pDog;
> X.print();
> }
> else if (I.Type == Cat)
> { // use I.pCat to access it
> auto& X = *I.pCat;
> X.print();
> }
>
> ...
> // end of code
>
>
