Blog post for Optional

Optional.hpp

auto nameByShirtNo = std::map<int, std::string>{{8, "Andres Iniesta"}};

const auto shirtNumber = 8;
const auto nameExists = nameByShirtNo.contains(shirtNumber);
if (nameExists)
{
    const auto playerName = nameByShirtNo.at(shirtNumber);
    std::cout << playerName << " wears shirt number " << shirtNumber;
} 
else
{
    std::cout << "Shirt number " << shirtNumber << " is not mapped to any player";
}

try
{
    auto playerName = nameByShirtNo.at(shirtNumber);
    std::cout << playerName << " wears shirt number " << shirtNumber;
} catch (const std::out_of_range&) 
{
    std::cout << "Shirt number " << shirtNumber << " is not mapped to any player";
}

const auto search = nameByShirtNo.find(shirtNumber);
if (search != nameByShirtNo.end()) {
    const auto playerName = search->second;
    std::cout << playerName << " wears shirt number " << shirtNumber;
} 
else
{
    std::cout << "Shirt number " << shirtNumber << " is not mapped to any player ";
}

std::optional<std::string> maybePlayerName(const int shirtNumber, const std::map<int, std::string> &nameByShirtNo)
{
    const auto search = nameByShirtNo.find(shirtNumber);
    if (search != nameByShirtNo.end())
    {
        return std::optional{search->second};
    }
    return std::nullopt;
}

const auto playerName = maybePlayerName(shirtNumber, nameByShirtNo);
if (playerName.has_value())
{
    std::cout << *playerName << " wears shirt number " << shirtNumber;
}
else
{
    std::cout << "Shirt number " << shirtNumber << " is not mapped to any player ";
}

tl::optional<std::string> maybePlayerName(const int shirtNumber, const std::map<int, std::string> &nameByShirtNo)
{
    const auto search = nameByShirtNo.find(shirtNumber);
    if (search != nameByShirtNo.end())
    {
        return search->second;
    }
    return tl::nullopt;
}

 maybePlayerName(shirtNumber, nameByShirtNo)
    .map([](const auto playerName) { std::cout << playerName << " wears shirt number " << shirtNumber; })
    .orElse([]{ std::cout << "Shirt number " << shirtNumber << " is not mapped to any player "; });

void printPlayerName(const std::string& playerName)
{
    std::cout << playerName << " was found!";
}

void printNoPlayerFound()
{
    std::cout << "No player found!";
}

 maybePlayerName(shirtNumber, nameByShirtNo)
    .map(printPlayerName)
    .orElse(printNoPlayerFound);

std::optional<int> maybePlayerAge(const std::string& playerName, const std::map<std::string, int> &ageByName)
{
    const auto search = ageByName.find(playerName);
    if (search != ageByName.end())
    {
        return search->second;
    }
    return std::nullopt;
}

auto isOlderThanThirty(const int currentAge)
{
    return currentAge>30;
}

const auto playerName = maybePlayerName(shirtNumber, nameByShirtNo);
if (playerName.has_value())
{
    const auto playerAge = maybePlayerAge(*playerName, ageByPlayerName);
    if (playerAge.has_value())
    {
        if (isOlderThanThirty(*playerAge))
        {
            std::cout << "Player with shirt number " << shirtNumber << 
            " is older 30";
        }
        else
        {
            std::cout << "Player with shirt number " << shirtNumber << 
            " is either not existing or younger than 31";
        }
    }
}

 maybePlayerName(shirtNumber, nameByShirtNo)
    .flatMap([&ageByPlayerName](auto playerName){ return maybePlayerAge(playerName, ageByPlayerName); })
    .filter(isOlderThanThirty)
    .map([](auto){std::cout << "Player with shirt number " << shirtNumber << 
                  " is older 30";})
    .orElse([]{ std::cout << "Player with shirt number " << shirtNumber << 
                 " is either not existing or younger than 31"; });