Hacking sum types with Go generics(blog.lawrencejones.dev)

    type OptionParser interface {
        ParseValue(data string) (*Value, error)
    }

    type OptionField struct {}

    func (of *OptionField) ParseValue(data string) (*Value, error) {
        return &Value{OptionID: data}, nil
    }

    type NumericField struct {}

    func (nf *NumericField) ParseValue(data string) (*Value, error) {
        value, err := strconv.ParseFloat(data, 64)
        if err != nil {
             return nil, errors.New("invalid value, must be a number")
        }

        return &Value{Numeric: value}, nil
    }