Re: [Cbor] Unusual map labels, dCBOR and interop

[Wolf McNally <[e-mail]>]

LL,

> On Mar 20, 2024, at 11:45 AM, lgl island-resort.com <[e-mail]> wrote:
> 
> dCBOR disallows the simple value “undefined” and NaN payloads (both are restrictions on the CBOR data model). I believe this is because JSON doesn’t support them. Seems logical that dCBOR might want to disallow maps and arrays as map keys since they are not supported in JSON.

Our design of dCBOR actually has little to do with JSON compatibility: our overriding concern has always been supporting determinism.

dCBOR’s numeric reduction as an analogue to JSON canonicalization of numeric values is a fairly obvious move (IMHO) and they dCBOR does share that in common with canonicalized forms of JSON. However, CBOR also supports NaN, while JSON does not, and as NaN is a useful value in many contexts, and also can easily be made canonical, we chose to include it. CBOR’s `undefined` being semantically indistinguishable from `null` for most practical purposes, and an obvious attempt to export an artifact of JavaScript into serialization, is something that we saw as a source of potential confusion when creating deterministic specifications, so we dropped `undefined`.

For most purposes I wouldn’t recommend map keys be complex. Nonetheless, I can definitely see reasons to have, for instance, vectors of various kinds be map keys. And again, JSON compatibility was a non-goal for dCBOR.

~ Wolf