amorfo77/json
1
0
Fork 0
mirror of https://github.com/nlohmann/json.git synced 2026-10-03 13:10:33 +00:00
Code Issues Packages Projects Releases Wiki Activity

Store maps with enum keys as objects (opt-in)

Browse Source 
Maps with enum keys, such as std::map<E, T>, are stored as arrays of
[key, value] pairs, because enums are not convertible to the string type
of object keys - even if NLOHMANN_JSON_SERIALIZE_ENUM maps them to
strings (#4378).

The new JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS macro stores them as objects
instead, converting each key with the enum's to_json. It applies to any
map-like type with enum keys (std::map with any comparator,
std::unordered_map, ...). A key that does not convert to a string throws
type_error.302, and two keys converting to the same string throw the new
type_error.318, rather than losing an entry. The macro changes the output
of inline functions, so it is part of the ABI tag (_ekmo).

Reading needs no macro: std::map and std::unordered_map with enum keys
are now also read from objects, converting each key with the enum's
from_json. That input was rejected before, and arrays of pairs are still
read, so data written either way can be read.

This supersedes #4531, which first proposed storing these maps as
objects.

Co-authored-by: Muhammad Amir bin Mohamad Ghazaly <amirghaz@umich.edu>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-27 17:48:58 +02:00
co-authored by Muhammad Amir bin Mohamad Ghazaly
parent 1e101ecac1
commit d914e3a027
22 changed files with 4553 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files
single_include/nlohmann/json.hpp
+96 -4
View File
@@ -103,6 +103,10 @@
#define JSON_STRICT_NUL_HANDLING 0
#endif
#ifndef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
#endif
#if JSON_DIAGNOSTICS
#define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
#else
@@ -139,14 +143,20 @@
#define NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING
#endif
#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
#define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS _ekmo
#else
#define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS
#endif
#ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
#define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
#endif
// Construct the namespace ABI tags component
#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f) json_abi ## a ## b ## c ## d ## e ## f
#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f) \
NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f)
#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g) json_abi ## a ## b ## c ## d ## e ## f ## g
#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g) \
NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g)
#define NLOHMANN_JSON_ABI_TAGS \
NLOHMANN_JSON_ABI_TAGS_CONCAT( \
@@ -155,7 +165,8 @@
NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS, \
NLOHMANN_JSON_ABI_TAG_BRACE_INIT_COPY_SEMANTICS, \
NLOHMANN_JSON_ABI_TAG_PRECISE_STREAM_POSITION, \
NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING)
NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING, \
NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS)
// Construct the namespace version component
#define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
@@ -4410,6 +4421,20 @@ template<typename BasicJsonType, typename CompatibleObjectType>
struct is_compatible_object_type
: is_compatible_object_type_impl<BasicJsonType, CompatibleObjectType> {};
// a map-like type (std::map, std::unordered_map, ...) whose keys are enums; see
// JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
template<typename T, typename = void>
struct is_enum_keyed_map : std::false_type {};
template<typename T>
struct is_enum_keyed_map <
T, enable_if_t < is_detected<mapped_type_t, T>::value&&
is_detected<key_type_t, T>::value >>
{
// NOLINTNEXTLINE(modernize-type-traits) we use C++11
static constexpr bool value = std::is_enum<typename T::key_type>::value;
};
template<typename BasicJsonType, typename ConstructibleObjectType,
typename = void>
struct is_constructible_object_type_impl : std::false_type {};
@@ -6047,11 +6072,40 @@ auto from_json(BasicJsonType&& j, TupleRelated&& t)
return from_json_tuple_impl(std::forward<BasicJsonType>(j), std::forward<TupleRelated>(t), priority_tag<3> {});
}
// read a map with enum keys from an object, using the enum's own from_json for
// the keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); this is the form written
// with JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
template<typename BasicJsonType, typename Map>
inline bool from_json_enum_keyed_object(const BasicJsonType& j, Map& m, std::true_type /*key is enum*/)
{
if (!j.is_object())
{
return false;
}
m.clear();
for (const auto& p : *j.template get_ptr<const typename BasicJsonType::object_t*>())
{
m.emplace(BasicJsonType(p.first).template get<typename Map::key_type>(), p.second.template get<typename Map::mapped_type>());
}
return true;
}
template<typename BasicJsonType, typename Map>
inline bool from_json_enum_keyed_object(const BasicJsonType& /*j*/, Map& /*m*/, std::false_type /*key is enum*/)
{
return false;
}
template < typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
typename = enable_if_t < !std::is_constructible <
typename BasicJsonType::string_t, Key >::value >>
inline void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allocator>& m)
{
// NOLINTNEXTLINE(modernize-type-traits) we use C++11
if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
{
return;
}
if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
{
JSON_THROW(type_error::create(302, concat("type must be array, but is ", j.type_name()), &j));
@@ -6072,6 +6126,11 @@ template < typename BasicJsonType, typename Key, typename Value, typename Hash,
typename BasicJsonType::string_t, Key >::value >>
inline void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyEqual, Allocator>& m)
{
// NOLINTNEXTLINE(modernize-type-traits) we use C++11
if (from_json_enum_keyed_object(j, m, std::is_enum<Key> {}))
{
return;
}
if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
{
JSON_THROW(type_error::create(302, concat("type must be array, but is ", j.type_name()), &j));
@@ -6167,6 +6226,8 @@ NLOHMANN_JSON_NAMESPACE_END
#include <valarray> // valarray
#include <vector> // vector
// #include <nlohmann/detail/exceptions.hpp>
// #include <nlohmann/detail/iterators/iteration_proxy.hpp>
// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++
@@ -6910,6 +6971,9 @@ template < typename BasicJsonType, typename CompatibleArrayType,
!is_basic_json<CompatibleArrayType>::value
#if JSON_HAS_RANGES && !defined(__MINGW32__)
&& !is_compatible_range_view<CompatibleArrayType>::value
#endif
#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
&& !is_enum_keyed_map<CompatibleArrayType>::value
#endif
,
int > = 0 >
@@ -6964,6 +7028,33 @@ inline void to_json(BasicJsonType& j, const CompatibleObjectType& obj)
external_constructor<value_t::object>::construct(j, obj);
}
#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
// store a map with enum keys as an object, using the enum's own to_json for the
// keys (e.g., from NLOHMANN_JSON_SERIALIZE_ENUM); without the macro, such maps
// are stored as arrays of [key, value] pairs
template < typename BasicJsonType, typename EnumKeyedMap,
enable_if_t < is_enum_keyed_map<EnumKeyedMap>::value&& !is_basic_json<EnumKeyedMap>::value, int > = 0 >
inline void to_json(BasicJsonType& j, const EnumKeyedMap& map)
{
typename BasicJsonType::object_t obj;
for (const auto& p : map)
{
BasicJsonType key = p.first;
if (JSON_HEDLEY_UNLIKELY(!key.is_string()))
{
JSON_THROW(type_error::create(302, concat("type must be string, but is ", key.type_name()), &key));
}
auto& key_string = *key.template get_ptr<typename BasicJsonType::string_t*>();
if (JSON_HEDLEY_UNLIKELY(!obj.emplace(key_string, BasicJsonType(p.second)).second))
{
JSON_THROW(type_error::create(318, concat("duplicate object key '", key_string, "'"), &key));
}
}
external_constructor<value_t::object>::construct(j, std::move(obj));
}
#endif
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
{
@@ -32549,6 +32640,7 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
#undef JSON_BRACE_INIT_COPY_SEMANTICS
#undef JSON_PRECISE_STREAM_POSITION
#undef JSON_STRICT_NUL_HANDLING
#undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
#endif
// #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
single_include/nlohmann/json_fwd.hpp
+15 -4
View File
@@ -64,6 +64,10 @@
#define JSON_STRICT_NUL_HANDLING 0
#endif
#ifndef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
#endif
#if JSON_DIAGNOSTICS
#define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
#else
@@ -100,14 +104,20 @@
#define NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING
#endif
#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
#define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS _ekmo
#else
#define NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS
#endif
#ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
#define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
#endif
// Construct the namespace ABI tags component
#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f) json_abi ## a ## b ## c ## d ## e ## f
#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f) \
NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f)
#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g) json_abi ## a ## b ## c ## d ## e ## f ## g
#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g) \
NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g)
#define NLOHMANN_JSON_ABI_TAGS \
NLOHMANN_JSON_ABI_TAGS_CONCAT( \
@@ -116,7 +126,8 @@
NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS, \
NLOHMANN_JSON_ABI_TAG_BRACE_INIT_COPY_SEMANTICS, \
NLOHMANN_JSON_ABI_TAG_PRECISE_STREAM_POSITION, \
NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING)
NLOHMANN_JSON_ABI_TAG_STRICT_NUL_HANDLING, \
NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS)
// Construct the namespace version component
#define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \