Json – failed to json.marshal map with non string keys

go, json

I want to convert a map[int]string to json, so I thought json.Marshal() would do the trick, but it fails saying unsupported type map[int]string. But whereas if I use a map with key string it works fine.

http://play.golang.org/p/qhlS9Nt8qQ

Later on inspection of the marshaller code, there is an explicit check to see if the key is not string and returns UnsupportedTypeError

Why can't I even use primitives as keys? If json standard doesn't allow non string keys, shouldn't json.Marshal convert the primitives to string and use them as keys ?

Best Solution

It's not because of Go, but because of Json: Json does not support anything else than strings for keys.

Have a look a the grammar of Json:

pair    string : valuestring    ""    " chars "

The full grammar is available on the Json website.

Unfortunately, to use integers as keys, you must convert them to string beforehand, for instance using strconv.Itoa: it is not up to the json package to do this work.