Go json Unmarshaller is not called

Question

I\'m fairly new to Golang. And I was looking for a way to do some custom stuff for marshaling and unmarshalling json. I have found the solution to implement M

Answer 1

You have a few distinct problems here.

• The method receiver must be a pointer if you want to modify the receiver, otherwise you're only modifying the copy local to the method.

• You always need to unmarshal into a pointer.

• You're declaring a "field" json tag for the Foo field, but passing in "foo"

• You're calling json.Unmarshal inside your UnmarshalJSON method, which is going to recurse indefinitely.

A working example would look like

func (d *Data) UnmarshalJSON(b []byte) error {
    type data Data
    tmp := &data{bar: "bar"}
    err := json.Unmarshal(b, tmp)
    if err != nil {
        return err
    }
    *d = Data(*tmp)
    return nil
}

func main() {
    jsonData := "{\"field\":\"test\"}"
    data := Data{}
    json.Unmarshal([]byte(jsonData), &data)
    fmt.Printf("%#v\n", data)
}

https://play.golang.org/p/FnF2li63dt

Answer 2

Data methods has value receiver, but the variable data has pointer type (*Data).

Pointer type variables cannot use functions with value receiver. Either change variable type or receiver type.

Also see https://github.com/golang/go/wiki/CodeReviewComments#receiver-type about receivers.