and<U>  method 
Returns a Result value as Err<U, E> if this Result is Err<T, E>,
otherwise returns other.
See also:
Rust: Result::and()
Implementation
Result<U, E> and<U>(Result<U, E> other) {
  return switch (this) {
    Ok() => other,
    Err(:E e) => Err(e),
  };
}