#pragma once
#include <array>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <limits>
#include <string>
#include <type_traits>
#include <nlohmann/detail/macro_scope.hpp>
#if JSON_HAS_THREE_WAY_COMPARISON
#include <compare>
#endif
NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{
@brief the JSON type enumeration
This enumeration collects the different JSON types. It is internally used to
distinguish the stored values, and the functions @ref basic_json::is_null(),
@ref basic_json::is_object(), @ref basic_json::is_array(),
@ref basic_json::is_string(), @ref basic_json::is_boolean(),
@ref basic_json::is_number() (with @ref basic_json::is_number_integer(),
@ref basic_json::is_number_unsigned(), and @ref basic_json::is_number_float()),
@ref basic_json::is_discarded(), @ref basic_json::is_primitive(), and
@ref basic_json::is_structured() rely on it.
@note There are three enumeration entries (number_integer, number_unsigned, and
number_float), because the library distinguishes these three types for numbers:
@ref basic_json::number_unsigned_t is used for unsigned integers,
@ref basic_json::number_integer_t is used for signed integers, and
@ref basic_json::number_float_t is used for floating-point numbers or to
approximate integers which do not fit in the limits of their respective type.
@sa see @ref basic_json::basic_json(const value_t value_type) -- create a JSON
value with the default value for a given type
@since version 1.0.0
*/
enum class value_t : std::uint8_t
{
null,
object,
array,
string,
boolean,
number_integer,
number_unsigned,
number_float,
binary,
discarded
};
@brief comparison operator for JSON types
Returns an ordering that is similar to Python:
- order: null < boolean < number < object < array < string < binary
- furthermore, each type is not smaller than itself
- discarded values are not comparable
- binary is represented as a b"" string in python and directly comparable to a
string; however, making a binary array directly comparable with a string would
be surprising behavior in a JSON file.
@since version 1.0.0
*/
#if JSON_HAS_THREE_WAY_COMPARISON
inline std::partial_ordering operator<=>(const value_t lhs, const value_t rhs) noexcept
#else
inline bool operator<(const value_t lhs, const value_t rhs) noexcept
#endif
{
static constexpr std::array<std::uint8_t, 9> order = {{
0 , 3 , 4 , 5 ,
1 , 2 , 2 , 2 ,
6
}
};
const auto l_index = static_cast<std::size_t>(lhs);
const auto r_index = static_cast<std::size_t>(rhs);
#if JSON_HAS_THREE_WAY_COMPARISON
if (l_index < order.size() && r_index < order.size())
{
return order[l_index] <=> order[r_index];
}
return std::partial_ordering::unordered;
#else
return l_index < order.size() && r_index < order.size() && order[l_index] < order[r_index];
#endif
}
#if JSON_HAS_THREE_WAY_COMPARISON && defined(__GNUC__)
inline bool operator<(const value_t lhs, const value_t rhs) noexcept
{
return std::is_lt(lhs <=> rhs);
}
#endif
@brief compare an integer with a floating point number without precision loss
Widening the integer to the floating point type loses precision beyond the
float's mantissa, which makes equality intransitive: both 2^63-2 and 2^63-1
round to 2^63, so each compares equal to that float while differing from each
other. Ordering built on that is not a strict weak ordering, so sorting such
values, or using them as keys in an ordered container, is undefined behavior.
Returns a value to be compared against zero with the original operator, which
reproduces the exact ordering. A NaN operand is returned as is, so comparing it
against zero keeps NaN's semantics: false for the relational operators and
unordered for `<=>`.
*/
template<typename IntegerType, typename FloatType>
FloatType compare_integer_with_float(const IntegerType i, const FloatType f) noexcept
{
const auto ordered = [](int c) noexcept
{
return static_cast<FloatType>(c);
};
if (std::isnan(f))
{
return f;
}
const FloatType bound = std::ldexp(static_cast<FloatType>(1), std::numeric_limits<IntegerType>::digits);
if (f >= bound)
{
return ordered(-1);
}
if (std::is_signed<IntegerType>::value ? (f < -bound) : (f < static_cast<FloatType>(0)))
{
return ordered(1);
}
const FloatType truncated = std::trunc(f);
const auto as_integer = static_cast<IntegerType>(truncated);
if (i != as_integer)
{
return ordered(i < as_integer ? -1 : 1);
}
const FloatType fraction = f - truncated;
if (fraction > static_cast<FloatType>(0))
{
return ordered(-1);
}
if (fraction < static_cast<FloatType>(0))
{
return ordered(1);
}
return ordered(0);
}
}
NLOHMANN_JSON_NAMESPACE_END