That's really neat, thanks (do you have any benchmarks comparing it to Go's JSON?), but doesn't cover my use case. I want all the values in a map-like API. I don't know anything about the shape of the contents, names of the keys, etc.
Looked at both. ffjson is a library that generates the marshaling/unmarshaling Go code for your structs, so it doesn't support my use case at all. megajson is abandonware ("This tool is unmaintained. Please use ffjson instead").
go-codec [1] is very good, and can do things like interning string keys to reduce allocation overhead, but it's not faster than encoding/json when working on plain maps.