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<?php date_default_timezone_set('Europe/London'); $date3 = DateTime::createFromFormat('Y-m-d H:i:s', '2019-04-01 00:00:00'); // 2019-04-01 00:00:00.0 Europe/London (+01:00) $date4 = clone $date3; $date4->modify('+5 week'); // 2019-05-06 00:00:00.0 Europe/London (+01:00) echo "So the originally modified date with 5 weeks added is:"; print_r($date4); echo "\n\n"; // positive DIFF and addition echo "1. positive DIFF and addition\n"; echo "diff is: "; $positiveDifferenceDateInterval2 = $date3->diff($date4); // interval: + 1m 4d; days 35 print_r($positiveDifferenceDateInterval2->format('%R %mm %dd')); echo "; days: {$positiveDifferenceDateInterval2->days} \n"; $positiveAddedDate = clone $date3; $positiveAddedDate->add($positiveDifferenceDateInterval2); print_r($positiveAddedDate); echo "is it equal to \$date4? "; var_dump($date4->getTimestamp() === $positiveAddedDate->getTimestamp()); echo "\n"; // negative DIFF and addition echo "2. negative DIFF and addition\n"; echo "diff is: "; $negativeDifferenceDateInterval2 = $date4->diff($date3); // interval: - 1m 5d; days 35 print_r($negativeDifferenceDateInterval2->format('%R %mm %dd')); echo "; days {$negativeDifferenceDateInterval2->days}"; $negativeAddedDate = clone $date3; // so in order to make it equal to $date4 I need to subtract a negative interval instead of adding a positive one? how crazy is that?! $negativeAddedDate->sub($negativeDifferenceDateInterval2); print_r($negativeAddedDate); echo "is it equal to \$date4? "; var_dump($date4->getTimestamp() === $negativeAddedDate->getTimestamp()); echo "\n\n"; echo 'So in order to make it equal to $date4 I need to subtract a negative interval instead of adding a positive one? How crazy is that?!';
based on JbKKW
Output for 7.1.25 - 7.4.0
So the originally modified date with 5 weeks added is:DateTime Object ( [date] => 2019-05-06 00:00:00.000000 [timezone_type] => 3 [timezone] => Europe/London ) 1. positive DIFF and addition diff is: + 1m 4d; days: 35 DateTime Object ( [date] => 2019-05-05 00:00:00.000000 [timezone_type] => 3 [timezone] => Europe/London ) is it equal to $date4? bool(false) 2. negative DIFF and addition diff is: - 1m 5d; days 35DateTime Object ( [date] => 2019-05-06 00:00:00.000000 [timezone_type] => 3 [timezone] => Europe/London ) is it equal to $date4? bool(true) So in order to make it equal to $date4 I need to subtract a negative interval instead of adding a positive one? How crazy is that?!