hash()

template<typename BasicJsonType >

std::size_t nlohmann::detail::hash

(

const BasicJsonType &

j

)

hash a JSON value

The hash function tries to rely on std::hash where possible. Furthermore, the type of the JSON value is taken into account to have different hash values for null, 0, 0U, and false, etc.

Template Parameters

BasicJsonType

basic_json specialization

Parameters

j	JSON value to hash

Returns

hash value of j

Definition at line 5240 of file json.hpp.

{
    using string_t = typename BasicJsonType::string_t;
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    const auto type = static_cast<std::size_t>(j.type());
 
    switch (j.type())
    {
        case BasicJsonType::value_t::null:
        case BasicJsonType::value_t::discarded:
        {
            return combine(type, 0);
        }
 
        case BasicJsonType::value_t::object:
        {
            auto seed = combine(type, j.size());
 
            for (const auto &element : j.items())
            {
                const auto h = std::hash<string_t> {}(element.key());
                seed = combine(seed, h);
                seed = combine(seed, hash(element.value()));
            }
 
            return seed;
        }
 
        case BasicJsonType::value_t::array:
        {
            auto seed = combine(type, j.size());
 
            for (const auto &element : j)
            {
                seed = combine(seed, hash(element));
            }
 
            return seed;
        }
 
        case BasicJsonType::value_t::string:
        {
            const auto h = std::hash<string_t> {}(j.template get_ref<const string_t &>());
            return combine(type, h);
        }
 
        case BasicJsonType::value_t::boolean:
        {
            const auto h = std::hash<bool> {}(j.template get<bool>());
            return combine(type, h);
        }
 
        case BasicJsonType::value_t::number_integer:
        {
            const auto h = std::hash<number_integer_t> {}(j.template get<number_integer_t>());
            return combine(type, h);
        }
 
        case BasicJsonType::value_t::number_unsigned:
        {
            const auto h = std::hash<number_unsigned_t> {}(j.template get<number_unsigned_t>());
            return combine(type, h);
        }
 
        case BasicJsonType::value_t::number_float:
        {
            const auto h = std::hash<number_float_t> {}(j.template get<number_float_t>());
            return combine(type, h);
        }
 
        case BasicJsonType::value_t::binary:
        {
            auto seed = combine(type, j.get_binary().size());
            const auto h = std::hash<bool> {}(j.get_binary().has_subtype());
            seed = combine(seed, h);
            seed = combine(seed, static_cast<std::size_t>(j.get_binary().subtype()));
 
            for (const auto byte : j.get_binary())
            {
                seed = combine(seed, std::hash<std::uint8_t> {}(byte));
            }
 
            return seed;
        }
 
        default:                   // LCOV_EXCL_LINE
            JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
            return 0;              // LCOV_EXCL_LINE
    }
}