Why 3 types of number?

[calebmer]

Just an innocent question, I'm curious to here the reason for three types (F64, U64, and I64) of what is ultimately typed in JSON as a number. This may betray the fact that I was never a low level programmer, but even if there is a low level reason I'd like to know it. Thanks for the great open source project 😊

[erickt]

Json doesn't define what a number means, so we err here on flexibility in order to avoid losing precision. If we only had a single f64 for our numbers, it could only precisely represent the integers up to -253 to 253. This protects us from, say, someone using a random u64 and an id.

One downside with our approach is that serde doesn't yet provide a good model for arbitrarily sized integers, so we cut things off at 64 bytes. If I recall correctly, this is the same behavior as RapidJSON and the various java parsers so I figured it wouldn't be a significant impact.

[calebmer]

Ok, thanks! 😊

[dtolnay]

I am not convinced by the justification. I filed #57 to follow up after #18 is resolved.

[dtolnay]

This was fixed in #188 / serde_json 0.9.0. Now there is one serde_json::Value::Number variant.