I needed to whip up a date delta (in my case, today minus 13 months) for SQL. I couldn't push the calculation onto the database, because the field in question is of type text rather than date, and converting it to a date and then subtracting the delta proved to be too expensive. Creating the date in Perl and using that is far more efficient. Don't blame me, I didn't design the schema, I just use it.

It's perhaps too-clever-by-half in that it's the most-commented bit of code I've written in some time, but I like the way it plays with list context.

use Date::Calc 'Add_Delta_YM';

my $date_limit = sprintf( '%02d-%02d-%04d',
    reverse               # Y M D --> D M Y
        sub {
            $_[5] + 1900, # year
            $_[4] +    1, # month
            $_[3],        # and day
                       0, # less this many years
                     -13, # and this many months
        }->(localtime),   # from today