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💡 add documentation

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Niels Lohmann 2020-07-15 13:45:16 +02:00
parent 496ddd127c
commit b821ed074f
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GPG key ID: 7F3CEA63AE251B69
3 changed files with 52 additions and 22 deletions
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35
include/nlohmann/detail/hash.hpp
View file

@ -1,6 +1,6 @@
#pragma once
#include <cstddef> // size_t
#include <cstddef> // size_t, uint8_t
#include <functional> // hash
namespace nlohmann
@ -8,12 +8,24 @@ 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)
{
@ -22,15 +34,18 @@ std::size_t hash(const BasicJsonType& j)
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(static_cast<std::size_t>(j.type()), 0);
{
return combine(type, 0);
}
case BasicJsonType::value_t::object:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
auto seed = combine(type, j.size());
for (const auto& element : j.items())
{
const auto h = std::hash<string_t> {}(element.key());
@ -42,7 +57,7 @@ std::size_t hash(const BasicJsonType& j)
case BasicJsonType::value_t::array:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
auto seed = combine(type, j.size());
for (const auto& element : j)
{
seed = combine(seed, hash(element));
@ -53,36 +68,36 @@ std::size_t hash(const BasicJsonType& j)
case BasicJsonType::value_t::string:
{
const auto h = std::hash<string_t> {}(j.template get_ref<const string_t&>());
return combine(static_cast<std::size_t>(j.type()), h);
return combine(type, h);
}
case BasicJsonType::value_t::boolean:
{
const auto h = std::hash<bool> {}(j.template get<bool>());
return combine(static_cast<std::size_t>(j.type()), h);
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(static_cast<std::size_t>(j.type()), h);
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(static_cast<std::size_t>(j.type()), h);
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(static_cast<std::size_t>(j.type()), h);
return combine(type, h);
}
case nlohmann::detail::value_t::binary:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.get_binary().size());
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());

35
single_include/nlohmann/json.hpp
View file

@ -4445,7 +4445,7 @@ class byte_container_with_subtype : public BinaryType
// #include <nlohmann/detail/hash.hpp>
#include <cstddef> // size_t
#include <cstddef> // size_t, uint8_t
#include <functional> // hash
namespace nlohmann
@ -4453,12 +4453,24 @@ 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)
{
@ -4467,15 +4479,18 @@ std::size_t hash(const BasicJsonType& j)
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(static_cast<std::size_t>(j.type()), 0);
{
return combine(type, 0);
}
case BasicJsonType::value_t::object:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
auto seed = combine(type, j.size());
for (const auto& element : j.items())
{
const auto h = std::hash<string_t> {}(element.key());
@ -4487,7 +4502,7 @@ std::size_t hash(const BasicJsonType& j)
case BasicJsonType::value_t::array:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
auto seed = combine(type, j.size());
for (const auto& element : j)
{
seed = combine(seed, hash(element));
@ -4498,36 +4513,36 @@ std::size_t hash(const BasicJsonType& j)
case BasicJsonType::value_t::string:
{
const auto h = std::hash<string_t> {}(j.template get_ref<const string_t&>());
return combine(static_cast<std::size_t>(j.type()), h);
return combine(type, h);
}
case BasicJsonType::value_t::boolean:
{
const auto h = std::hash<bool> {}(j.template get<bool>());
return combine(static_cast<std::size_t>(j.type()), h);
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(static_cast<std::size_t>(j.type()), h);
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(static_cast<std::size_t>(j.type()), h);
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(static_cast<std::size_t>(j.type()), h);
return combine(type, h);
}
case nlohmann::detail::value_t::binary:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.get_binary().size());
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());

4
test/src/unit-hash.cpp
View file

@ -54,7 +54,7 @@ TEST_CASE("hash")
hashes.insert(std::hash<json> {}(json("foo")));
// number
hashes.insert(std::hash<json> {}(json(int(0))));
hashes.insert(std::hash<json> {}(json(0)));
hashes.insert(std::hash<json> {}(json(unsigned(0))));
hashes.insert(std::hash<json> {}(json(-1)));
@ -81,4 +81,4 @@ TEST_CASE("hash")
hashes.insert(std::hash<json> {}(json(json::value_t::discarded)));
CHECK(hashes.size() == 21);
}
}