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Search once for a new object member in unflatten() and j[json_pointer]

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object_member() looked a key up and, if it was missing, inserted it with
operator[], which searches again. Objects that can find the position of a
key and insert there (std::map) now do both with one search; other object
types are unchanged. A key that exists is not copied, as before.

unflatten() (instructions on macOS, Linux Ir GCC 13 / Clang 18): twitter 25.8M ->
24.2M, 24.9M -> 21.8M / 24.8M -> 21.5M; citm_catalog 43.4M -> 43.5M, 38.9M ->
37.0M / 39.6M -> 37.5M; canada unchanged.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-22 09:29:59 +02:00
1 parent f930ed5f71
commit a89d3d2738
2 files changed
+52 -2
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include/nlohmann/detail/json_pointer.hpp
+26 -1
View File
@@ -482,8 +482,27 @@ class json_pointer
}
/// @brief object member access with a key that is only copied if it is inserted
///
/// Objects that can find the position of a key and insert there
/// (std::map) search once, others look the key up and add it if it is missing.
template<typename BasicJsonType>
static BasicJsonType& object_member(BasicJsonType& object, const string_t& key)
static auto object_member_impl(BasicJsonType& object, const string_t& key, detail::priority_tag<1> /*unused*/)
-> decltype(object.m_data.m_value.object->emplace_hint(object.m_data.m_value.object->lower_bound(key), key, nullptr), std::declval<BasicJsonType&>())
{
auto& members = *object.m_data.m_value.object;
auto it = members.lower_bound(key);
if (it != members.end() && !members.key_comp()(key, it->first))
{
return it->second;
}
const auto old_capacity = object.container_capacity();
it = members.emplace_hint(it, key, nullptr);
return object.set_parent_after_insert(it->second, old_capacity);
}
template<typename BasicJsonType>
static BasicJsonType& object_member_impl(BasicJsonType& object, const string_t& key, detail::priority_tag<0> /*unused*/)
{
auto& members = *object.m_data.m_value.object;
const auto it = members.find(key);
@@ -494,6 +513,12 @@ class json_pointer
return object.operator[](key);
}
template<typename BasicJsonType>
static BasicJsonType& object_member(BasicJsonType& object, const string_t& key)
{
return object_member_impl(object, key, detail::priority_tag<1> {});
}
JSON_PRIVATE_UNLESS_TESTED:
json_pointer top() const
{
single_include/nlohmann/json.hpp
Generated
+26 -1
View File
@@ -22832,8 +22832,27 @@ class json_pointer
}
/// @brief object member access with a key that is only copied if it is inserted
///
/// Objects that can find the position of a key and insert there
/// (std::map) search once, others look the key up and add it if it is missing.
template<typename BasicJsonType>
static BasicJsonType& object_member(BasicJsonType& object, const string_t& key)
static auto object_member_impl(BasicJsonType& object, const string_t& key, detail::priority_tag<1> /*unused*/)
-> decltype(object.m_data.m_value.object->emplace_hint(object.m_data.m_value.object->lower_bound(key), key, nullptr), std::declval<BasicJsonType&>())
{
auto& members = *object.m_data.m_value.object;
auto it = members.lower_bound(key);
if (it != members.end() && !members.key_comp()(key, it->first))
{
return it->second;
}
const auto old_capacity = object.container_capacity();
it = members.emplace_hint(it, key, nullptr);
return object.set_parent_after_insert(it->second, old_capacity);
}
template<typename BasicJsonType>
static BasicJsonType& object_member_impl(BasicJsonType& object, const string_t& key, detail::priority_tag<0> /*unused*/)
{
auto& members = *object.m_data.m_value.object;
const auto it = members.find(key);
@@ -22844,6 +22863,12 @@ class json_pointer
return object.operator[](key);
}
template<typename BasicJsonType>
static BasicJsonType& object_member(BasicJsonType& object, const string_t& key)
{
return object_member_impl(object, key, detail::priority_tag<1> {});
}
JSON_PRIVATE_UNLESS_TESTED:
json_pointer top() const
{