Arbitrary precision numbers

[dtolnay]

Fixes #18.

serde_json = { version = "0.9", features = ["arbitrary_precision"] }

#[derive(Serialize, Deserialize)]
struct S {
    n: serde_json::Number,
    v: serde_json::Value,
}

let s: S = serde_json::from_str(...)?;

// full precision
println!("{}", s.n);
println!("{}", s.v);
println!("{}", serde_json::to_string(&s)?);

[dtolnay]

@alexreg please take a quick look at this and let us know whether it satisfies your use case.

[alexreg]

A few name changes I would suggest for clarity/consistency:

ParseNumber -> Json(Number)Visitor
VisitNumber -> (Number)Visitor
SerializeNumber -> NumberSerializer

Take them or leave them. :)

[dtolnay]

Thanks for the idea. I would prefer to leave it as is. We use ...Visitor for things that implement the Visitor trait and ...Serializer for things that implement the Serializer trait, which is not the case here.

[dtolnay]

Waiting on #18 (comment).

[alexreg]

Fair enough.

[dtolnay]

I am going to try to rework this to use the same trick that TOML uses for specialized handling of Datetimes without relying on specialization.

[alexreg]

If it's using a "trick", I'd be very much against that! Nothing too hacky, please.

[dtolnay]

Let's call it "under-explored abilities of the API" rather than "trick."

[alexreg]

Okay. I quite like the way it worked currently... so I hope it doesn't change too much!

[alexreg]

Any update on this yet, @dtolnay?

[dtolnay]

Nope, will be post 1.0.

[alexreg]

Okay. No chance of getting a feature-gated specialisation-based version before then? I don't know when 1.0 will be, but I guess soon-ish...

[dtolnay]

No chance of getting a feature-gated specialization-based version. We are making some lifetime-related changes in the next release (#288) and specialization interacts very poorly with lifetimes - use after free, corrupted data, etc. See rust-lang/rust#40582.

[alexreg]

@dtolnay How about now? :)