Private fields bugs when renaming

[gobigshark]

Failed to support private fields when renaming.

`package main

import (
"fmt"

jsoniter "github.com/json-iterator/go"
"github.com/json-iterator/go/extra"

)

func main() {
extra.SupportPrivateFields()
type TestObject struct {
field string json:"myfield"
}
obj := TestObject{}
jsoniter.UnmarshalFromString({"myfield":"Hello"}, &obj)
fmt.Println(obj.field) // Output empty string instead of "Hello"
}`

[ceshihao]

It is because your field field is unexported. It is introduced by #175

@taowen said

if field is unexported, the field names will be empty slice. field names are used to decode or encode one go field from multiple json field. if is empty, meaning it is not present in json.

I am wondering whether unexported field need to be support if using the private field extension?

[yuyistudio]

I thought extra.SupportPrivateFields() meant that the export of private fields were fully supported. Still don't get the idea why the rename of private fields are designed to be forbidden, which means lower-camel-case style is now a unpleasant compulsion for all exported JSON data of my program.