How to copy an interface value in Go?

Question

How to copy an interface value in Go?

My User interface:

type User interface {
    Name() string
    SetName(name string)
}

Answer 1

There is a more generic way to do that.

func Clone(oldObj interface{}) interface{} {
    newObj := reflect.New(reflect.TypeOf(oldObj).Elem())
    oldVal := reflect.ValueOf(oldObj).Elem()
    newVal := newObj.Elem()
    for i := 0; i < oldVal.NumField(); i++ {
        newValField := newVal.Field(i)
        if newValField.CanSet() {
            newValField.Set(oldVal.Field(i))
        }
    }

    return newObj.Interface()
}

However, it has one pitfall: it cannot set unexported fields. It can be worked around using this solution with the help of unsafe's black magic, but I would rather avoid it.