In other words, this is a flattened alternative to UnwrapOr(T).
var or = Ok(42).Or(Ok(7));
Assert.Equal(Ok(42), or);
or = Ok(42).Or(Err<int>("error-message"));
Assert.Equal(Ok(42), or);
or = Err<int>("error-message").Or(Ok(7));
Assert.Equal(Ok(7), or);
or = Err<int>("error-message").Or(Err<int>("second-error-message"));
Assert.True(or.IsErr);
Assert.Equal(Some("second-error-message"), or.ErrorMessage());
public Res<T> Or(
Res<T> other
)