PHP 数组转XML 格式

function buildXml( $data, $wrap= 'xml' ){
    $str = "<{$wrap}>";
    if( is_array( $data ) ){
         if( hasIndex( $data ) ){
            foreach( $data as $k=>$v ){
                 $str .= buildXml( $v, $k );
            }
         }else{
            foreach( $data as $v ){
                foreach( $v as $k1=>$v1 )
                $str .= buildXml( $v1, $k1 );
            }
         }
    }else
        $str .= $data;
    $str .= "</{$wrap}>";
    return $str;
}

function hasIndex( $arr ){
    return array_keys($arr) !== range(0, count($arr) - 1);
}
$arr1 = [
    'title'=>'title',
    'bbb'=>[
        'AAA'=>12,
        'BBB'=>555
    ]
];
$arr2 = [
    'aaa'=>1,
    'bbb'=>[
        ['AAA'=>[
            'BBB'=>[
                ['DDDD'=>111],['DDDD'=>222]
            ]
        ]],
        ['AAA'=>6]
    ]
];
header("Content-type: text/xml");
echo '<?xml version="1.0" encoding="utf-8"?>';
echo buildXml($arr2);