JSON v2

[Som-Som-CC]

At the time of writing JSON v2 is still experimental. But it is really promising.

• It is safer. E.g. throws an error on duplicate fields and case-sensitive by default.
• It is much faster when using interfaces, when the new v2 functions are used, e.g. json.UnmarshalRead(r.Body, &val) or json.MarshalWrite(w, &val). The performance gain is application dependent, expected to be around 3-fold.

In the meanwhile, Restful's experimental MessagePack support could be deprecated. It failed to deliver the performance gains we hoped for.