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Only track the target key order in diff() for insertion-ordered objects

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common_keys_target_order and new_keys_form_suffix are only read when object_t keeps its members in insertion order; skip building them otherwise. Addresses review comment by @gregmarr.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-30 07:33:13 +02:00
parent 9802542843
commit c109e260df
2 changed files with 34 additions and 18 deletions
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include/nlohmann/json.hpp
+17 -9
View File
@@ -6150,12 +6150,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
// the same time, determine whether every added key comes // the same time, determine whether every added key comes
// after every common key in target's order (a precondition // after every common key in target's order (a precondition
// for the fast path below, which only ever appends new keys // for the fast path below, which only ever appends new keys
// at the very end): for an object_t whose iteration order is // at the very end). Both are only needed for an object_t that
// a pure function of the key set (e.g. the default std::map, // keeps its members in insertion order, such as the one
// which always iterates in sorted key order), the order // backing `ordered_json`; for any other object_t, the fast
// check further below is always true and this whole // path is always taken and they are not computed.
// mechanism is effectively a no-op; it only matters for a
// reorderable object_t such as the one backing `ordered_json`.
// patch ops for keys that were added (i.e., in target but not // patch ops for keys that were added (i.e., in target but not
// in source); built here so the fast path below can reuse // in source); built here so the fast path below can reuse
// them without a second source.find() per target key. Only // them without a second source.find() per target key. Only
@@ -6179,11 +6177,21 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
} }
else else
{ {
common_keys_target_order.push_back(it.key()); #ifdef JSON_HEDLEY_MSVC_VERSION
if (seen_new_key) #pragma warning(push )
#pragma warning(disable : 4127) // ignore warning to replace if with if constexpr
#endif
if (detail::is_ordered_map<object_t>::value)
{ {
new_keys_form_suffix = false; common_keys_target_order.push_back(it.key());
if (seen_new_key)
{
new_keys_form_suffix = false;
}
} }
#ifdef JSON_HEDLEY_MSVC_VERSION
#pragma warning( pop )
#endif
} }
} }
single_include/nlohmann/json.hpp
+17 -9
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@@ -32231,12 +32231,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
// the same time, determine whether every added key comes // the same time, determine whether every added key comes
// after every common key in target's order (a precondition // after every common key in target's order (a precondition
// for the fast path below, which only ever appends new keys // for the fast path below, which only ever appends new keys
// at the very end): for an object_t whose iteration order is // at the very end). Both are only needed for an object_t that
// a pure function of the key set (e.g. the default std::map, // keeps its members in insertion order, such as the one
// which always iterates in sorted key order), the order // backing `ordered_json`; for any other object_t, the fast
// check further below is always true and this whole // path is always taken and they are not computed.
// mechanism is effectively a no-op; it only matters for a
// reorderable object_t such as the one backing `ordered_json`.
// patch ops for keys that were added (i.e., in target but not // patch ops for keys that were added (i.e., in target but not
// in source); built here so the fast path below can reuse // in source); built here so the fast path below can reuse
// them without a second source.find() per target key. Only // them without a second source.find() per target key. Only
@@ -32260,11 +32258,21 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
} }
else else
{ {
common_keys_target_order.push_back(it.key()); #ifdef JSON_HEDLEY_MSVC_VERSION
if (seen_new_key) #pragma warning(push )
#pragma warning(disable : 4127) // ignore warning to replace if with if constexpr
#endif
if (detail::is_ordered_map<object_t>::value)
{ {
new_keys_form_suffix = false; common_keys_target_order.push_back(it.key());
if (seen_new_key)
{
new_keys_form_suffix = false;
}
} }
#ifdef JSON_HEDLEY_MSVC_VERSION
#pragma warning( pop )
#endif
} }
} }