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Make the value lifecycle inline-friendly

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Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-15 11:46:15 +02:00
1 parent ebab8a11cc
commit 106065e62d
4 files changed
+586 -104
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include/nlohmann/json.hpp
+146 -52
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@@ -585,26 +585,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
switch (t)
{
case value_t::object:
{
object = create<object_t>();
break;
}
case value_t::array:
{
array = create<array_t>();
break;
}
case value_t::string:
{
string = create<string_t>("");
break;
}
case value_t::binary:
{
binary = create<binary_t>();
// allocating: kept out of line, so the scalar cases below inline
init_owned(t);
break;
}
@@ -651,6 +637,34 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
}
}
JSON_HEDLEY_NEVER_INLINE
void init_owned(value_t t)
{
switch (t)
{
case value_t::object:
object = create<object_t>();
break;
case value_t::array:
array = create<array_t>();
break;
case value_t::string:
string = create<string_t>("");
break;
case value_t::binary:
binary = create<binary_t>();
break;
case value_t::null:
case value_t::boolean:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
case value_t::discarded:
default:
break;
}
}
/// constructor for strings
json_value(const string_t& value) : string(create<string_t>(value)) {}
@@ -911,7 +925,18 @@ public:
}
}
// only strings, binaries, arrays and objects own memory; keep the
// check for them inline so destroying a scalar is a compare and a
// branch, and leave the actual work to an out-of-line function
void destroy(value_t t)
{
if (JSON_HEDLEY_UNLIKELY(t == value_t::string || t == value_t::binary || t == value_t::object || t == value_t::array))
{
destroy_owned(t);
}
}
JSON_HEDLEY_NEVER_INLINE void destroy_owned(value_t t)
{
switch (t)
{
@@ -2559,15 +2584,15 @@ public:
// check of passed value is valid
other.assert_invariant();
if (m_data.m_type == value_t::object || m_data.m_type == value_t::array)
if (JSON_HEDLEY_LIKELY(m_data.m_type != value_t::object && m_data.m_type != value_t::array
&& m_data.m_type != value_t::string && m_data.m_type != value_t::binary))
{
// copying the container directly would call this constructor again
// for every element, once per nesting level
copy_structured(other);
// null, boolean, numbers, discarded: plain copy of the union
m_data.m_value = other.m_data.m_value;
}
else
{
copy_leaf_value(other, *this);
copy_owning(other);
}
assert_invariant();
@@ -2799,6 +2824,22 @@ public:
// value access //
//////////////////
/// out-of-line part of the copy constructor for owning types
JSON_HEDLEY_NEVER_INLINE
void copy_owning(const basic_json& other)
{
if (m_data.m_type == value_t::object || m_data.m_type == value_t::array)
{
// copying the container directly would call this constructor again
// for every element, once per nesting level
copy_structured(other);
}
else
{
copy_leaf_value(other, *this);
}
}
/// get a pointer to the value (object)
object_t* get_impl_ptr(object_t* /*unused*/) noexcept
{
@@ -5173,6 +5214,20 @@ public:
/// @name lexicographical comparison operators
/// @{
// the same-type cases for non-owning scalars, shared by JSON_IMPLEMENT_OPERATOR
// and JSON_IMPLEMENT_SCALAR_FAST
#define JSON_IMPLEMENT_SCALAR_CASES(op, null_result) \
case value_t::null: \
return (null_result); \
case value_t::boolean: \
return (lhs.m_data.m_value.boolean) op (rhs.m_data.m_value.boolean); \
case value_t::number_integer: \
return (lhs.m_data.m_value.number_integer) op (rhs.m_data.m_value.number_integer); \
case value_t::number_unsigned: \
return (lhs.m_data.m_value.number_unsigned) op (rhs.m_data.m_value.number_unsigned); \
case value_t::number_float: \
return (lhs.m_data.m_value.number_float) op (rhs.m_data.m_value.number_float);
// note parentheses around operands are necessary; see
// https://github.com/nlohmann/json/issues/1530
// Mixed signed/unsigned integer comparisons check whether the signed value
@@ -5209,24 +5264,11 @@ public:
return (*lhs.m_data.m_value.object) op (*rhs.m_data.m_value.object); \
} \
\
case value_t::null: \
return (null_result); \
\
JSON_IMPLEMENT_SCALAR_CASES(op, null_result) \
\
case value_t::string: \
return (*lhs.m_data.m_value.string) op (*rhs.m_data.m_value.string); \
\
case value_t::boolean: \
return (lhs.m_data.m_value.boolean) op (rhs.m_data.m_value.boolean); \
\
case value_t::number_integer: \
return (lhs.m_data.m_value.number_integer) op (rhs.m_data.m_value.number_integer); \
\
case value_t::number_unsigned: \
return (lhs.m_data.m_value.number_unsigned) op (rhs.m_data.m_value.number_unsigned); \
\
case value_t::number_float: \
return (lhs.m_data.m_value.number_float) op (rhs.m_data.m_value.number_float); \
\
case value_t::binary: \
return (*lhs.m_data.m_value.binary) op (*rhs.m_data.m_value.binary); \
\
@@ -5270,6 +5312,24 @@ public:
\
return (default_result);
// inline fast path for two values of the same non-owning scalar type; anything
// else falls through to the out-of-line general comparison
#define JSON_IMPLEMENT_SCALAR_FAST(op, null_result) \
if (lhs.m_data.m_type == rhs.m_data.m_type) \
{ \
switch (lhs.m_data.m_type) \
{ \
JSON_IMPLEMENT_SCALAR_CASES(op, null_result) \
case value_t::object: \
case value_t::array: \
case value_t::string: \
case value_t::binary: \
case value_t::discarded: \
default: \
break; \
} \
}
JSON_PRIVATE_UNLESS_TESTED:
// returns true if:
// - any operand is NaN and the other operand is of number type
@@ -5297,6 +5357,46 @@ public:
return compares_unordered(*this, rhs, inverse);
}
// out-of-line general comparisons; the operators below handle same-type
// scalars inline and fall through to these
JSON_HEDLEY_NEVER_INLINE
static bool equal_general(const_reference lhs, const_reference rhs) noexcept
{
#ifdef __GNUC__
JSON_HEDLEY_DIAGNOSTIC_PUSH
JSON_HEDLEY_PRAGMA(GCC diagnostic ignored "-Wfloat-equal")
#endif
JSON_IMPLEMENT_OPERATOR( ==, true, false, false,
compare_iteratively<false>(lhs, rhs, false) == compare_result::equal, true)
#ifdef __GNUC__
JSON_HEDLEY_DIAGNOSTIC_POP
#endif
}
JSON_HEDLEY_NEVER_INLINE
static bool less_general(const_reference lhs, const_reference rhs) noexcept
{
// default_result is used if we cannot compare values. In that case,
// we compare types. Note we have to call the operator explicitly,
// because MSVC has problems otherwise.
JSON_IMPLEMENT_OPERATOR( <, false, false, operator<(lhs_type, rhs_type),
compare_iteratively<true>(lhs, rhs, true) == compare_result::less, false)
}
#if JSON_HAS_THREE_WAY_COMPARISON
JSON_HEDLEY_NEVER_INLINE
static std::partial_ordering three_way_general(const_reference lhs, const_reference rhs) noexcept // *NOPAD*
{
// default_result is used if we cannot compare values. In that case,
// we compare types.
JSON_IMPLEMENT_OPERATOR(<=>, // *NOPAD*
std::partial_ordering::equivalent,
std::partial_ordering::unordered,
lhs_type <=> rhs_type, // *NOPAD*
to_partial_ordering(compare_iteratively<true>(lhs, rhs, false)), true)
}
#endif
public:
#if JSON_HAS_THREE_WAY_COMPARISON
/// @brief comparison: equal
@@ -5308,11 +5408,11 @@ public:
JSON_HEDLEY_PRAGMA(GCC diagnostic ignored "-Wfloat-equal")
#endif
const_reference lhs = *this;
JSON_IMPLEMENT_OPERATOR( ==, true, false, false,
compare_iteratively<false>(lhs, rhs, false) == compare_result::equal, true)
JSON_IMPLEMENT_SCALAR_FAST( ==, true)
#ifdef __GNUC__
JSON_HEDLEY_DIAGNOSTIC_POP
#endif
return equal_general(lhs, rhs);
}
/// @brief comparison: equal
@@ -5329,13 +5429,8 @@ public:
std::partial_ordering operator<=>(const_reference rhs) const noexcept // *NOPAD*
{
const_reference lhs = *this;
// default_result is used if we cannot compare values. In that case,
// we compare types.
JSON_IMPLEMENT_OPERATOR(<=>, // *NOPAD*
std::partial_ordering::equivalent,
std::partial_ordering::unordered,
lhs_type <=> rhs_type, // *NOPAD*
to_partial_ordering(compare_iteratively<true>(lhs, rhs, false)), true)
JSON_IMPLEMENT_SCALAR_FAST(<=>, std::partial_ordering::equivalent) // *NOPAD*
return three_way_general(lhs, rhs);
}
/// @brief comparison: 3-way
@@ -5423,11 +5518,11 @@ public:
JSON_HEDLEY_DIAGNOSTIC_PUSH
JSON_HEDLEY_PRAGMA(GCC diagnostic ignored "-Wfloat-equal")
#endif
JSON_IMPLEMENT_OPERATOR( ==, true, false, false,
compare_iteratively<false>(lhs, rhs, false) == compare_result::equal, true)
JSON_IMPLEMENT_SCALAR_FAST( ==, true)
#ifdef __GNUC__
JSON_HEDLEY_DIAGNOSTIC_POP
#endif
return equal_general(lhs, rhs);
}
// The friend comparisons with a scalar name the JSON type via decltype of
@@ -5482,11 +5577,8 @@ public:
/// @sa https://json.nlohmann.me/api/basic_json/operator_lt/
friend bool operator<(const_reference lhs, const_reference rhs) noexcept
{
// default_result is used if we cannot compare values. In that case,
// we compare types. Note we have to call the operator explicitly,
// because MSVC has problems otherwise.
JSON_IMPLEMENT_OPERATOR( <, false, false, operator<(lhs_type, rhs_type),
compare_iteratively<true>(lhs, rhs, true) == compare_result::less, false)
JSON_IMPLEMENT_SCALAR_FAST( <, false)
return less_general(lhs, rhs);
}
/// @brief comparison: less than
@@ -5597,6 +5689,8 @@ public:
#endif
#undef JSON_IMPLEMENT_OPERATOR
#undef JSON_IMPLEMENT_SCALAR_FAST
#undef JSON_IMPLEMENT_SCALAR_CASES
/// @}