date-diff.php

<?php
  $date1 = DateTimeImmutable::createFromFormat('Y-m-d','2012-12-01');
  $date2 = DateTimeImmutable::createFromFormat('Y-m-d H:i:s','2012-12-10 12:00:00');
  dd([
      $date1->diff($date2)->invert, // 0
      $date2->diff($date1)->invert, // 1
      $date1->diff($date2)->format('%d'), // "8"
      $date2->diff($date1)->format('%d'), // "8"
      (int)$date2->diff($date1)->format('%R%a'), // -8
      (int)$date1->diff($date2)->format('%R%a') // 8
  ]);