如何从c++中的函数返回不同的类型？

#include <iostream>

class Base {
public:
    virtual ~Base() {}
    virtual void print() const = 0;
};

class Derived1 : public Base {
public:
    void print() const override {
        std::cout << "Derived1" << std::endl;
    }
};

class Derived2 : public Base {
public:
    void print() const override {
        std::cout << "Derived2" << std::endl;
    }
};

Base* create(int type) {
    switch (type) {
        case 1: return new Derived1();
        case 2: return new Derived2();
        default: return nullptr;
    }
}

int main() {
    Base* b1 = create(1);
    Base* b2 = create(2);
    b1->print(); // 输出 "Derived1"
    b2->print(); // 输出 "Derived2"
    delete b1;
    delete b2;
    return 0;
}

#include <iostream>
#include <variant>

int add(int a, int b) {
    return a + b;
}

std::string greet(const std::string& name) {
    return "Hello, " + name + "!";
}

std::variant<int, std::string> calculateOrGreet(bool isAddition, int a, int b, const std::string& name) {
    if (isAddition) {
        return add(a, b);
    } else {
        return greet(name);
    }
}

int main() {
    auto result1 = calculateOrGreet(true, 3, 4, "");
    auto result2 = calculateOrGreet(false, 0, 0, "World");

    if (std::holds_alternative<int>(result1)) {
        std::cout << "Result: " << std::get<int>(result1) << std::endl; // 输出 "Result: 7"
    }

    if (std::holds_alternative<std::string>(result2)) {
        std::cout << "Result: " << std::get<std::string>(result2) << std::endl; // 输出 "Result: Hello, World!"
    }

    return 0;
}

#include <iostream>
#include <any>

int add(int a, int b) {
    return a + b;
}

std::string greet(const std::string& name) {
    return "Hello, " + name + "!";
}

std::any calculateOrGreet(bool isAddition, int a, int b, const std::string& name) {
    if (isAddition) {
        return add(a, b);
    } else {
        return greet(name);
    }
}

int main() {
    auto result1 = calculateOrGreet(true, 3, 4, "");
    auto result2 = calculateOrGreet(false, 0, 0, "World");

    if (result1.type() == typeid(int)) {
        std::cout << "Result: " << std::any_cast<int>(result1) << std::endl; // 输出 "Result: 7"
    }

    if (result2.type() == typeid(std::string)) {
        std::cout << "Result: " << std::any_cast<std::string>(result2) << std::endl; // 输出 "Result: Hello, World!"
    }

    return 0;
}

#include <iostream>
#include <functional>

int add(int a, int b) {
    return a + b;
}

std::string greet(const std::string& name) {
    return "Hello, " + name + "!";
}

std::function<void()> getFunction(bool isAddition, int a, int b, const std::string& name) {
    if (isAddition) {
        int result = add(a, b);
        return [result]() { std::cout << "Result: " << result << std::endl; };
    } else {
        std::string result = greet(name);
        return [result]() { std::cout << "Result: " << result << std::endl; };
    }
}

int main() {
    auto func1 = getFunction(true, 3, 4, "");
    auto func2 = getFunction(false, 0, 0, "World");

    func1(); // 输出 "Result: 7"
    func2(); // 输出 "Result: Hello, World!"

    return 0;
}