C++ (Cpp) optional::front示例

std::vector<std::string> Exchange::extractBoundaries(
    const boost::optional<std::vector<BSONObj>>& obj, Ordering ordering) {
    std::vector<std::string> ret;

    if (!obj) {
        return ret;
    }

    for (auto& b : *obj) {
        // Build the key.
        BSONObjBuilder kb;
        for (auto elem : b) {
            kb << "" << elem;
        }

        KeyString key{KeyString::Version::V1, kb.obj(), ordering};
        std::string keyStr{key.getBuffer(), key.getSize()};

        ret.emplace_back(std::move(keyStr));
    }

    uassert(50960, str::stream() << "Exchange range boundaries are not valid", ret.size() > 1);

    for (size_t idx = 1; idx < ret.size(); ++idx) {
        uassert(50893,
                str::stream() << "Exchange range boundaries are not in ascending order.",
                ret[idx - 1] < ret[idx]);
    }

    BSONObjBuilder kbMin;
    BSONObjBuilder kbMax;
    for (int i = 0; i < obj->front().nFields(); ++i) {
        kbMin << "" << MINKEY;
        kbMax << "" << MAXKEY;
    }

    KeyString minKey{KeyString::Version::V1, kbMin.obj(), ordering};
    KeyString maxKey{KeyString::Version::V1, kbMax.obj(), ordering};
    StringData minKeyStr{minKey.getBuffer(), minKey.getSize()};
    StringData maxKeyStr{maxKey.getBuffer(), maxKey.getSize()};

    uassert(50958,
            str::stream() << "Exchange lower bound must be the minkey.",
            ret.front() == minKeyStr);
    uassert(50959,
            str::stream() << "Exchange upper bound must be the maxkey.",
            ret.back() == maxKeyStr);

    return ret;
}