#include <string>

#include <functional>

#include <iostream>

#include <optional>

// optional can be used as the return type of a factory that may fail

std::optional<std::string> create(bool b) {

if (b)

return "Godzilla";

return {};

}

// std::nullopt can be used to create any (empty) std::optional

auto create2(bool b) {

return b ? std::optional<std::string>{"Godzilla"} : std::nullopt;

}

// std::reference_wrapper may be used to return a reference

auto create_ref(bool b) {

static std::string value = "Godzilla";

return b ? std::optional<std::reference_wrapper<std::string>>{value}

: std::nullopt;

}

int main()

{

std::cout << "create(false) returned "

<< create(false).value_or("empty") << '\n';

// optional-returning factory functions are usable as conditions of while and if

if (auto str = create2(true)) {

std::cout << "create2(true) returned " << *str << '\n';

}

if (auto str = create_ref(true)) {

// using get() to access the reference_wrapper's value

std::cout << "create_ref(true) returned " << str->get() << '\n';

str->get() = "Mothra";

std::cout << "modifying it changed it to " << str->get() << '\n';

}

}