Question

$currentDT = new \DateTime(); 
$filterRange = new \DateInterval('PT30S'); 
$filterDate = $currentDT->sub($filterRange); 
var_dump($currentDT); 
var_dump($filterDate);

OUTPUT:

object(DateTime)[246]
  public 'date' => string '2011-12-10 15:53:42' (length=19)
  public 'timezone_type' => int 3
  public 'timezone' => string 'America/New_York' (length=16)
object(DateTime)[246]
  public 'date' => string '2011-12-10 15:53:42' (length=19)
  public 'timezone_type' => int 3
  public 'timezone' => string 'America/New_York' (length=16)

$currentDT and $filterDate are the same…even though they should be 30s different. Any idea why?

Answer 1

That is the expected behaviour, the subtraction acts on the original object which is then returned. This can be seen by the 246 in the var_dump() outputs, denoting that they’re one and the same object.

If you wish to keep the original object untouched, you’ll need to clone it before doing the subtraction.

$currentDT   = new \DateTime('2011-12-13 14:15:16');
$filterRange = new \DateInterval('PT30S');
$filterDate  = clone $currentDT;
$filterDate->sub($filterRange);
var_dump($currentDT, $filterDate);