php - Negative DateInterval

Question

I want to create a DatePeriod object with a negative DateInterval.

This creates a DatePeriod with the year increasing from today to 2016.

$this->Set('dates', new DatePeriod(new DateTime(), new DateInterval('P1Y'), new DateTime('2016-06-06')));

I want to start at 2016, and using a negative DateInterval move towards todays year

Something like this might illustrate my desire

$this->Set('dates', new DatePeriod(new DateTime('2016-06-06'), new DateInterval('-P1Y'), new DateTime()));

I just can't find any extended info on either DatePeriod or DateInterval on how to do this. All i find is that DateInterval can be inverted.

Answer 1

According to comment by kevinpeno at 17-Mar-2011 07:47 on php.net's page about DateInterval::__construct(), you cannot directly create negative DateIntervals through the constructor:

new DateInterval('-P1Y'); // Exception "Unknown or bad format (-P1Y)"

Instead of this you are required to create a positive interval and explicitly set it's invert property to 1:

$di = new DateInterval('P1Y');
$di->invert = 1; // Proper negative date interval

Just checked the above code by myself, it's working exactly in this way.