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2.4.5: keep the inlined number cases in from_json(ArithmeticType&) (#5891)

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Calling get_number_value() from from_json(ArithmeticType&) made
GetArray<std::array<int, 1000>> 2.4x slower (it changes the inlining of the
std::array conversion), so that overload keeps its own switch, with a comment.
get_arithmetic_value() still uses the shared helper.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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Niels Lohmann committed 2026-10-23 12:00:39 +02:00
1 parent bf27f0ba99
commit 96b5c82496
1 file changed
+37 -8
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include/nlohmann/detail/conversions/from_json.hpp
+37 -8
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@@ -437,17 +437,46 @@ template < typename BasicJsonType, typename ArithmeticType,
int > = 0 >
inline void from_json(const BasicJsonType& j, ArithmeticType& val)
{
if (get_number_value(j, val))
// the number cases repeat get_number_value() on purpose: calling it here
// changes the inlining of get<T>() in the std::array conversion, which then
// runs 2.4x slower (GetArray benchmark, #5891); unlike get_arithmetic_value(),
// a boolean is accepted
switch (static_cast<value_t>(j))
{
return;
}
case value_t::number_unsigned:
{
// never null: a basic_json whose number_unsigned_t is number_integer_t
// stores no number_unsigned values (#2573)
const auto* ptr = j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>();
JSON_ASSERT(ptr != nullptr);
val = static_cast<ArithmeticType>(*ptr);
break;
}
case value_t::number_integer:
{
val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_integer_t*>());
break;
}
case value_t::number_float:
{
val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_float_t*>());
break;
}
case value_t::boolean:
{
val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::boolean_t*>());
break;
}
// unlike get_arithmetic_value(), a boolean is accepted here
if (JSON_HEDLEY_UNLIKELY(!j.is_boolean()))
{
throw_type_must_be("number", j);
case value_t::null:
case value_t::object:
case value_t::array:
case value_t::string:
case value_t::binary:
case value_t::discarded:
default:
throw_type_must_be("number", j);
}
val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::boolean_t*>());
}
template<typename BasicJsonType, typename Type>