Question

Is there a technical reason why unexported fields are not included by encoding/json? If not and it is an arbitrary decision could there be an additional back door option (say ‘+’) to include even though unexported?

Requiring client code to export to get this functionality feels unfortunate, especially if lower case is providing encapsulation or the decision to marshal structures comes much later than design of them.

How are people dealing with this? Just export everything?

Also, doesn’t exporting field names make it difficult to follow suggested idioms. I think if a struct X has field Y, you can not have an accessor method Y(). If you want to provide interface access to Y you have to come up with a new name for the getter and no matter what you’ll get something un-idiomatic according to http://golang.org/doc/effective_go.html#Getters

Answer 1

There is a technical reason. The json library does not have the power to view fields using reflect unless they are exported. A package can only view the unexported fields of types within its own package

In order to deal with your problem, what you can do is make an unexported type with exported fields. Json will unmarshal into an unexported type if passed to it without a problem but it would not show up in the API docs. You can then make an exported type that embeds the unexported type. This exported type would then need methods to implement the json.Marshaler and json.Unmarshaler interfaces.

Note: all code is untested and may not even compile.

type jsonData struct {
    Field1 string
    Field2 string
}

type JsonData struct {
    jsonData
}

// Implement json.Unmarshaller
func (d *JsonData) UnmarshalJSON(b []byte) error {
    return json.Unmarshal(b, &d.jsonData)
}

// Getter
func (d *JsonData) Field1() string {
    return d.jsonData.Field1
}