diff --git a/include/nlohmann/detail/hash.hpp b/include/nlohmann/detail/hash.hpp
new file mode 100644
index 00000000..d3313e96
--- /dev/null
+++ b/include/nlohmann/detail/hash.hpp
@@ -0,0 +1,117 @@
+#pragma once
+
+#include <cstddef> // size_t, uint8_t
+#include <functional> // hash
+
+namespace nlohmann
+{
+namespace detail
+{
+
+// boost::hash_combine
+std::size_t combine(std::size_t seed, std::size_t h) noexcept
+{
+ seed ^= h + 0x9e3779b9 + (seed << 6U) + (seed >> 2U);
+ return seed;
+}
+
+/*!
+@brief 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.
+
+@tparam BasicJsonType basic_json specialization
+@param j JSON value to hash
+@return hash value of j
+*/
+template<typename BasicJsonType>
+std::size_t hash(const BasicJsonType& j)
+{
+ 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 nlohmann::detail::value_t::number_unsigned:
+ {
+ const auto h = std::hash<number_unsigned_t> {}(j.template get<number_unsigned_t>());
+ return combine(type, h);
+ }
+
+ case nlohmann::detail::value_t::number_float:
+ {
+ const auto h = std::hash<number_float_t> {}(j.template get<number_float_t>());
+ return combine(type, h);
+ }
+
+ case nlohmann::detail::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, 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); // LCOV_EXCL_LINE
+ }
+}
+
+} // namespace detail
+} // namespace nlohmann
diff --git a/include/nlohmann/json.hpp b/include/nlohmann/json.hpp
index 7c2cf2b1..1a45b776 100644
--- a/include/nlohmann/json.hpp
+++ b/include/nlohmann/json.hpp
@@ -51,6 +51,7 @@ SOFTWARE.
#include <nlohmann/detail/conversions/from_json.hpp>
#include <nlohmann/detail/conversions/to_json.hpp>
#include <nlohmann/detail/exceptions.hpp>
+#include <nlohmann/detail/hash.hpp>
#include <nlohmann/detail/input/binary_reader.hpp>
#include <nlohmann/detail/input/input_adapters.hpp>
#include <nlohmann/detail/input/lexer.hpp>
@@ -8698,9 +8699,7 @@ struct hash<nlohmann::json>
*/
std::size_t operator()(const nlohmann::json& j) const
{
- // a naive hashing via the string representation
- const auto& h = hash<nlohmann::json::string_t>();
- return h(j.dump());
+ return nlohmann::detail::hash(j);
}
};
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 32986cb6..7f59aca2 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -4442,6 +4442,125 @@ class byte_container_with_subtype : public BinaryType
// #include <nlohmann/detail/exceptions.hpp>
+// #include <nlohmann/detail/hash.hpp>
+
+
+#include <cstddef> // size_t, uint8_t
+#include <functional> // hash
+
+namespace nlohmann
+{
+namespace detail
+{
+
+// boost::hash_combine
+std::size_t combine(std::size_t seed, std::size_t h) noexcept
+{
+ seed ^= h + 0x9e3779b9 + (seed << 6U) + (seed >> 2U);
+ return seed;
+}
+
+/*!
+@brief 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.
+
+@tparam BasicJsonType basic_json specialization
+@param j JSON value to hash
+@return hash value of j
+*/
+template<typename BasicJsonType>
+std::size_t hash(const BasicJsonType& j)
+{
+ 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 nlohmann::detail::value_t::number_unsigned:
+ {
+ const auto h = std::hash<number_unsigned_t> {}(j.template get<number_unsigned_t>());
+ return combine(type, h);
+ }
+
+ case nlohmann::detail::value_t::number_float:
+ {
+ const auto h = std::hash<number_float_t> {}(j.template get<number_float_t>());
+ return combine(type, h);
+ }
+
+ case nlohmann::detail::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, 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); // LCOV_EXCL_LINE
+ }
+}
+
+} // namespace detail
+} // namespace nlohmann
+
// #include <nlohmann/detail/input/binary_reader.hpp>
@@ -24653,9 +24772,7 @@ struct hash<nlohmann::json>
*/
std::size_t operator()(const nlohmann::json& j) const
{
- // a naive hashing via the string representation
- const auto& h = hash<nlohmann::json::string_t>();
- return h(j.dump());
+ return nlohmann::detail::hash(j);
}
};
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 9146d43b..91ff5a21 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -112,6 +112,7 @@ set(files
src/unit-deserialization.cpp
src/unit-element_access1.cpp
src/unit-element_access2.cpp
+ src/unit-hash.cpp
src/unit-inspection.cpp
src/unit-items.cpp
src/unit-iterators1.cpp
diff --git a/test/src/unit-hash.cpp b/test/src/unit-hash.cpp
new file mode 100644
index 00000000..186cad88
--- /dev/null
+++ b/test/src/unit-hash.cpp
@@ -0,0 +1,84 @@
+/*
+ __ _____ _____ _____
+ __| | __| | | | JSON for Modern C++ (test suite)
+| | |__ | | | | | | version 3.8.0
+|_____|_____|_____|_|___| https://github.com/nlohmann/json
+
+Licensed under the MIT License <http://opensource.org/licenses/MIT>.
+SPDX-License-Identifier: MIT
+Copyright (c) 2013-2019 Niels Lohmann <http://nlohmann.me>.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using json = nlohmann::json;
+
+#include <set>
+
+TEST_CASE("hash")
+{
+ // Collect hashes for different JSON values and make sure that they are distinct
+ // We cannot compare against fixed values, because the implementation of
+ // std::hash may differ between compilers.
+
+ std::set<std::size_t> hashes;
+
+ // null
+ hashes.insert(std::hash<json> {}(json(nullptr)));
+
+ // boolean
+ hashes.insert(std::hash<json> {}(json(true)));
+ hashes.insert(std::hash<json> {}(json(false)));
+
+ // string
+ hashes.insert(std::hash<json> {}(json("")));
+ hashes.insert(std::hash<json> {}(json("foo")));
+
+ // number
+ hashes.insert(std::hash<json> {}(json(0)));
+ hashes.insert(std::hash<json> {}(json(unsigned(0))));
+
+ hashes.insert(std::hash<json> {}(json(-1)));
+ hashes.insert(std::hash<json> {}(json(0.0)));
+ hashes.insert(std::hash<json> {}(json(42.23)));
+
+ // array
+ hashes.insert(std::hash<json> {}(json::array()));
+ hashes.insert(std::hash<json> {}(json::array({1, 2, 3})));
+
+ // object
+ hashes.insert(std::hash<json> {}(json::object()));
+ hashes.insert(std::hash<json> {}(json::object({{"foo", "bar"}})));
+
+ // binary
+ hashes.insert(std::hash<json> {}(json::binary({})));
+ hashes.insert(std::hash<json> {}(json::binary({}, 0)));
+ hashes.insert(std::hash<json> {}(json::binary({}, 42)));
+ hashes.insert(std::hash<json> {}(json::binary({1, 2, 3})));
+ hashes.insert(std::hash<json> {}(json::binary({1, 2, 3}, 0)));
+ hashes.insert(std::hash<json> {}(json::binary({1, 2, 3}, 42)));
+
+ // discarded
+ hashes.insert(std::hash<json> {}(json(json::value_t::discarded)));
+
+ CHECK(hashes.size() == 21);
+}