Challenge 2: Fixing the Diamond With virtual Inheritance — Possible Solution
====================================================================

#include <iostream>
#include <string>

class Animal {
public:
    std::string name;
};

class Swimmer : virtual public Animal {};
class Flyer : virtual public Animal {};

class Duck : public Swimmer, public Flyer {};

int main() {
    Duck d;
    d.name = "Donald";
    std::cout << d.name << std::endl;
    return 0;
}

Output:

    Donald

WHY THIS WORKS AS AN ANSWER
------------------------------
Adding virtual to BOTH Swimmer's and Flyer's own inheritance from
Animal (per the chapter's own warn-box, both paths must agree) means
Duck now contains exactly ONE shared Animal sub-object instead of two
-- d.name unambiguously refers to that single shared name field, so
the assignment and the subsequent read both compile and produce the
expected result, resolving the exact ambiguity Challenge 1
demonstrated.