ADT in C++. Based on https://dev.to/tmr232/that-overloaded-trick-overloading-lambdas-in-c17

sumtype.cpp

template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;

template<class Variant, class... Ts>
auto match(Variant v, Ts... matchers) {
    return visit(overloaded{matchers...}, v);
}

struct Human {string name; int age;};
struct Animal {string kind; int age;};
using Species = variant<Human, Animal>;

int main() {
    Species species = Human{"John", 100};

    // example 1
    visit(
        overloaded{
            [](Human const & human) {
                cout << "Human name: " << human.name << endl;
            },
            [](Animal const & animal) {
                cout << "Animal kind: " << animal.kind << endl;
            },
        },
        species
    );
    
    // example 2
    match(
        species,
        [](Human const & human) {
            cout << "Human name: " << human.name << endl;
        },
        [](Animal const & animal) {
            cout << "Animal kind: " << animal.kind << endl;
        }
    );

    // example 3
    cout
        <<  match(
                species,
                [](Human  human ){return "Human name: "  + human .name;},
                [](Animal animal){return "Animal kind: " + animal.kind;}
            )
        <<  endl;
}