Let's do it the other way around: currently the month is set to 2. We try to set day to 30, but the system won't allow it, because the 30th of February isn't valid. We were going to set the month later, you bozo system!

Lesson to be learned: don't let the system do your thinking.

I don't like overzealous range testing for each individual field, in this example because the ranges themselves are interdependent. Having a get/set interface won't help one single bit.

Instead, I only want the system to check if the date is valid, when I'm trying to use the date (in case of a Javascript on a HTML form: when trying to submit the form). In perl, for often used checks, you still can have some speed boost by caching, either by checking if the date has changed since last time, before checking again, or some use of a Memoize cache on the function value.