php 中 debug_zval_dump 用法

$a = array(1,2,3);// 如果是数字，就不支持foreach($a as $k => $v){    $t = $v;    debug_zval_dump($v);// 数字直接显示数字}echo "<hr >";$b = array('1','2','3');//字符串才可以foreach($b as $k => $v){    $t = $v;    debug_zval_dump($v);}echo "<hr >";$c = array('1','2','3');foreach($c as $k => &$v){    $t = $v;    debug_zval_dump($v);}echo "<hr >";$var1 = 'Hello World';$var2 = '';$var2 =$var1;debug_zval_dump($var1);