问题:

Any variable in this object is !isset() but if I either var_dump($interval) or print_r($interval), these variables becomes isset(). This also applies to empty()/!empty().

So in the code below $interval->i is initially !isset() but isset() after I var_dump($interval).

$future = new DateTime("2018-08-24");
$now = new DateTime();

$interval = $future->diff($now);

if (isset($interval->i)) {
    echo 'isset' . $interval->i;
} else {
    echo 'not isset' . $interval->i;
}

var_dump($interval);

if (isset($interval->i)) {
    echo 'isset' . $interval->i;
} else {
    echo 'not isset' . $interval->i;
}

What could possibly be causing these to be !isset and empty initially, but isset and !empty afterwards?