Parsing of negative zero

[6502]

I noticed that parsing -0 results in 0, is this intentional or just happened? I saw nothing in the documentation or in the issue list about it...

[nlohmann]

Number handling is described in https://json.nlohmann.me/features/types/number_handling/ - apparently, -0 is allowed, but is treated like 0 by this library. What would you expect instead?

[6502]

-0.0 parses as negative zero (yes, IEEE754 has negative zero that is distinct from zero - even if they must compare equal with ==). I'm not opinionated on this but found this little difference between your parser and mine (and JSON formally doesn't know what an integer is)

[6502]

By the way checking other libraries seems this is a very common behavior (for example both rapidjson and the json parser of the standard library of python do the same). I would say that parsing -0 as zero (and instead -0.0 as negative zero) is incorrect (in other words I see a similar case for e.g. 9999999999999999999999999... if the number cannot be represented correctly as an int you parse it as a double; -0 cannot be represented as an int, so I'd say should be represented in a double). JSON is however about interoperability first, so if most other libraries are parsing -0 as 0 (throwing away the negative information) then may be it is a better idea even if IMO more confused and questionable in abstract given that JSON knows nothing about integer/float differences. If you like I can propose a documentation integration for at least describing this behavior.

[nlohmann]

I would add the following paragraph to the documentation

---

Zeros

The JSON number grammar allows for different ways to express zero, and this library will store zeros differently:

Literal	Stored value and type	Serialization
0	std::uint64_t(0)	0
-0	std::int64_t(0)	0
0.0	double(0.0)	0.0
-0.0	double(-0.0)	-0.0
0E0	double(0.0)	0.0
-0E0	double(-0.0)	-0.0

That is, -0 is stored as a signed integer, but the serialization does not reproduce the -.

[6502]

That clarifies and indeed even allows to distinguish 0 and -0 in the improbable case someone actually cares. In other words the information is not actually lost as I originally thought. 👍