PHP如何动态为多维数组的子数组分别添加元素

PHP如何动态为多维数组的子数组分别添加元素,如下：
问题：$a=array(0=>array("name"=>"a","mail"=>"b"),1=>array("name"=>"d","mail"=>"e"))怎样可以变成array(0=>array("name"=>"a","mail"=>"b"，tel=>"k"),1=>array("name"=>"d","mail"=>"e" tel=>"e"))方法$a=array(0=>array("name"=>"a","mail"=>"b"),1=>array("name"=>"d","mail"=>"e"));

function addkey(&$val, $key, $param)
{
 $val[$param['key']] = $param['val'];
}

array_walk($a,'addkey',array('key'=>'tel', 'val'=>'123'));
print_r($a);

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