How to avoid Copy constructor doing object slicing

Question

Refer code below:

I have reference to base class and hence it should not result into object slicing. But it seems slicing is done due to copy constructor. How can we avoid this?
https://sololearn.com/compiler-playground/cO9TSqCIFbma/?ref=app

Answer 1

don't use auto, it resolves to Animal. you want Animal&.
or you can use auto&. This resolve to Animal&

void TestMethod(Animal& animal)
{
Animal& copiedAnimal = animal;
copiedAnimal.display();
}

Answer 2

Thanks Bob_Li