php实践，static静态变量如何作为函数多次调用的共享变量？

class S{
    const A ="sunan大叔";    
    static $a ="苏南大叔";
    public $b ="普通变量";
}
echo S::A;     // 这里是个常量
echo S::$a;
// echo S::$b; // error

sunan大叔
苏南大叔

function sunan($x)
{
    static $all = [];
    echo count($all);
    $key = str_repeat($x,count($all)+1);
    $all[$key] = $x;
    return $all;
}
sunan("a");
sunan("b");
sunan("b");
$all = sunan("c");
var_dump($all);

0123
array(4) {
  ["a"]=>
  string(1) "a"
  ["bb"]=>
  string(1) "b"
  ["bbb"]=>
  string(1) "b"
  ["cccc"]=>
  string(1) "c"
}

class N {
    const AAA = "苏南大叔加油！";
    static $aaa="==========";
    public static function test(){
        static $cnt = 0;
        $cnt ++;
        static::$aaa = str_repeat(self::AAA,$cnt);
        return $cnt;
    }
}
N::test();
N::test();
N::test();
echo N::$aaa;

苏南大叔加油！苏南大叔加油！苏南大叔加油！

class SN
{
    public static $attr="sunan大叔";
    public static function test(){
        echo "苏南大叔",PHP_EOL;
    }
}
echo SN::$attr,PHP_EOL;
$sn = new SN;
echo $sn::$attr,PHP_EOL;
echo $sn->$attr,PHP_EOL;  // 这个输出为空
SN::test();
$sn::test();
$sn->test();

sunan大叔
sunan大叔

苏南大叔
苏南大叔
苏南大叔