Optional Results

std::optional represents a result that might not exist.

optional_results.cpp

#include <iostream>
#include <optional>
#include <string>
#include <vector>

std::optional<int> findPrice(const std::vector<std::pair<std::string, int>>& prices,
                             const std::string& item) {
    for (const auto& entry : prices) {
        if (entry.first == item) {
            return entry.second;
        }
    }
    return std::nullopt;
}

int main() {
    std::vector<std::pair<std::string, int>> prices{{"pencil", 2}, {"notebook", 5}};
    std::string item = ;

    std::optional<int> price = findPrice(prices, item);

    std::cout << "item=" << item << std::endl;
    if (price.has_value()) {
        std::cout << "price=" << price.value() << std::endl;
    } else {
        std::cout << "price=missing" << std::endl;
    }
    return 0;
}

#include <iostream>
#include <optional>
#include <string>
#include <vector>

std::optional<int> findPrice(const std::vector<std::pair<std::string, int>>& prices,
                             const std::string& item) {
    for (const auto& entry : prices) {
        if (entry.first == item) {
            return entry.second;
        }
    }
    return std::nullopt;
}

int main() {
    std::vector<std::pair<std::string, int>> prices{{"pencil", 2}, {"notebook", 5}};
    std::string item = ;

    std::optional<int> price = findPrice(prices, item);

    std::cout << "item=" << item << std::endl;
    if (price.has_value()) {
        std::cout << "price=" << price.value() << std::endl;
    } else {
        std::cout << "price=missing" << std::endl;
    }
    return 0;
}

#include <iostream>
#include <optional>
#include <string>
#include <vector>

std::optional<int> findPrice(const std::vector<std::pair<std::string, int>>& prices,
                             const std::string& item) {
    for (const auto& entry : prices) {
        if (entry.first == item) {
            return entry.second;
        }
    }
    return std::nullopt;
}

int main() {
    std::vector<std::pair<std::string, int>> prices{{"pencil", 2}, {"notebook", 5}};
    std::string item = ;

    std::optional<int> price = findPrice(prices, item);

    std::cout << "item=" << item << std::endl;
    if (price.has_value()) {
        std::cout << "price=" << price.value() << std::endl;
    } else {
        std::cout << "price=missing" << std::endl;
    }
    return 0;
}

optional result An optional result makes the missing case visible without inventing a fake value.