pointers - What is the difference between reflect.ValueOf() and Value.Elem() in go?

Question

I started learning golang a couple of days ago and found reflect.Valueof() and Value.Elem() quite confusing. What is the difference between this two function/methods and how to use them correctly?

Both function/methods return a Value, and according to the go doc

ValueOf returns a new Value initialized to the concrete value stored in the interface i. ValueOf(nil) returns the zero Value.

Elem returns the value that the interface v contains or that the pointer v points to. It panics if v's Kind is not Interface or Ptr. It returns the zero Value if v is nil.

I found this code from a post on stackoverflow but still don't understand when to use .Elem()

func SetField(obj interface{}, name string, value interface{}) error {
    
    // won't work if I remove .Elem()
    structValue := reflect.ValueOf(obj).Elem()
    
    structFieldValue := structValue.FieldByName(name)

    if !structFieldValue.IsValid() {
        return fmt.Errorf("No such field: %s in obj", name)
    }

    if !structFieldValue.CanSet() {
        return fmt.Errorf("Cannot set %s field value", name)
    }

    structFieldType := structFieldValue.Type()

    // won't work either if I add .Elem() to the end
    val := reflect.ValueOf(value)
    if structFieldType != val.Type() {

        return fmt.Errorf("Provided value %v type %v didn't match obj field type %v",val,val.Type(),structFieldType)
    }

    structFieldValue.Set(val)
    return nil
}

Answer 1

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