PHP 语法糖

if (time() % 2) {
    $b = '111';
} else {
    $b = '222';
}

$b = time() % 2 ? '111' : '222';

$a = new stdClass();
if (null !== $a) {
   $b = $a->name;
} else {
   $b = null;
}

$a = new stdClass();
$b = $a?->name;

if (isset($a)) {
  $a = 'default';
}

echo $a;

echo $a ?? 'default';

['a' => $a, 0 => $b] = ['a' => 123, 456]
// $a = 123 , $b = 456