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Merged
nlohmann merged 2 commits into from
Oct 15, 2026
Merged

Speed up container destruction, iterator access and diff() #5835

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de54d33
Speed up container destruction, iterator access and diff()
nlohmann Oct 15, 2026
8aeb14e
Destroy the first levels of a value by recursion
nlohmann Oct 15, 2026
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183 changes: 59 additions & 124 deletions include/nlohmann/detail/iterators/iter_impl.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -294,40 +294,25 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
{
JSON_ASSERT(m_object != nullptr);

switch (m_object->m_data.m_type)
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))

@gregmarr gregmarr Oct 15, 2026

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Why duplicate the code from the switch here? Was this supposed to be a move? If so, why?

@nlohmann nlohmann Oct 15, 2026

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Written by Claude Code on behalf of @nlohmann. You're right, the duplication was unintended: it is now a move (commit 7cc6f32). The array/object branches sit in front of the switch so the hot path inlines (range-for over an array 2.5 → 1.3 ns/element); the switch bodies for those cases are gone, and what remained only handled primitives, so it is now plain code. No behaviour change.

{
case value_t::object:
{
JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
return m_it.object_iterator->second;
}

case value_t::array:
{
JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
return *m_it.array_iterator;
}

case value_t::null:
throw_cannot_get_value();
JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
return *m_it.array_iterator;
}

case value_t::string:
case value_t::boolean:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
case value_t::binary:
case value_t::discarded:
default:
{
if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
{
return *m_object;
}
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
{
JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
return m_it.object_iterator->second;
}

throw_cannot_get_value();
}
// neither array nor object: a primitive value (null has no value to point to)
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type != value_t::null && m_it.primitive_iterator.is_begin()))
{
return *m_object;
}

throw_cannot_get_value();
}

/*!
Expand All @@ -338,38 +323,25 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
{
JSON_ASSERT(m_object != nullptr);

switch (m_object->m_data.m_type)
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))

@gregmarr gregmarr Oct 15, 2026

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Why duplicate the code from the switch here? Was this supposed to be a move? If so, why?

@nlohmann nlohmann Oct 15, 2026

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Written by Claude Code on behalf of @nlohmann. You're right, the duplication was unintended: it is now a move (commit 7cc6f32). The array/object branches sit in front of the switch so the hot path inlines (range-for over an array 2.5 → 1.3 ns/element); the switch bodies for those cases are gone, and what remained only handled primitives, so it is now plain code. No behaviour change.

{
case value_t::object:
{
JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
return &(m_it.object_iterator->second);
}

case value_t::array:
{
JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
return &*m_it.array_iterator;
}
JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
return &*m_it.array_iterator;
}

case value_t::null:
case value_t::string:
case value_t::boolean:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
case value_t::binary:
case value_t::discarded:
default:
{
if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
{
return m_object;
}
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
{
JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
return &(m_it.object_iterator->second);
}

throw_cannot_get_value();
}
// neither array nor object: a primitive value
if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
{
return m_object;
}

throw_cannot_get_value();
}

/*!
Expand All @@ -391,35 +363,20 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
{
JSON_ASSERT(m_object != nullptr);

switch (m_object->m_data.m_type)
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))

@gregmarr gregmarr Oct 15, 2026

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Why duplicate the code from the switch here? Was this supposed to be a move? If so, why?

@nlohmann nlohmann Oct 15, 2026

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Written by Claude Code on behalf of @nlohmann. You're right, the duplication was unintended: it is now a move (commit 7cc6f32). The array/object branches sit in front of the switch so the hot path inlines (range-for over an array 2.5 → 1.3 ns/element); the switch bodies for those cases are gone, and what remained only handled primitives, so it is now plain code. No behaviour change.

{
case value_t::object:
{
std::advance(m_it.object_iterator, 1);
break;
}

case value_t::array:
{
std::advance(m_it.array_iterator, 1);
break;
}
++m_it.array_iterator;
return *this;
}

case value_t::null:
case value_t::string:
case value_t::boolean:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
case value_t::binary:
case value_t::discarded:
default:
{
++m_it.primitive_iterator;
break;
}
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
{
std::advance(m_it.object_iterator, 1);
return *this;
}

// neither array nor object: a primitive value
++m_it.primitive_iterator;
return *this;
}

Expand All @@ -442,35 +399,20 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
{
JSON_ASSERT(m_object != nullptr);

switch (m_object->m_data.m_type)
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))
{
case value_t::object:
{
std::advance(m_it.object_iterator, -1);
break;
}

case value_t::array:
{
std::advance(m_it.array_iterator, -1);
break;
}
--m_it.array_iterator;
return *this;
}

case value_t::null:
case value_t::string:
case value_t::boolean:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
case value_t::binary:
case value_t::discarded:
default:
{
--m_it.primitive_iterator;
break;
}
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
{
std::advance(m_it.object_iterator, -1);
return *this;
}

// neither array nor object: a primitive value
--m_it.primitive_iterator;
return *this;
}

Expand All @@ -493,25 +435,18 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
return true;
}

switch (m_object->m_data.m_type)
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))

@gregmarr gregmarr Oct 15, 2026

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Why duplicate the code from the switch here? Was this supposed to be a move? If so, why?

@nlohmann nlohmann Oct 15, 2026

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Written by Claude Code on behalf of @nlohmann. You're right, the duplication was unintended: it is now a move (commit 7cc6f32). The array/object branches sit in front of the switch so the hot path inlines (range-for over an array 2.5 → 1.3 ns/element); the switch bodies for those cases are gone, and what remained only handled primitives, so it is now plain code. No behaviour change.

{
case value_t::object:
return (m_it.object_iterator == other.m_it.object_iterator);

case value_t::array:
return (m_it.array_iterator == other.m_it.array_iterator);
return (m_it.array_iterator == other.m_it.array_iterator);
}

case value_t::null:
case value_t::string:
case value_t::boolean:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
case value_t::binary:
case value_t::discarded:
default:
return (m_it.primitive_iterator == other.m_it.primitive_iterator);
if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
{
return (m_it.object_iterator == other.m_it.object_iterator);
}

// neither array nor object: a primitive value
return (m_it.primitive_iterator == other.m_it.primitive_iterator);
}

/*!
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