函数的结果怎么赋值给变量啊

Question

<?php
  $name = 'stefen';
  $tel = '10795856';
  $motto = 'If you shed tears when you miss the sun,then you would miss the stars';

  function totalLen(...$string){
    //=print_r($string);
    foreach ($string as $content) {
      echo strlen($content).',';
    }
  }

  $arrNum = totalLen($name,$tel,$motto);
  //totalLen($name,$tel,$motto)会得到6,8,69，但是貌似不能赋值给$arrNum

  echo array_sum(array($arrNum));

我想实现的功能是，无论有多少变量传入函数，都能自动计算出所有字符的长度的和，但是现在没办法把得到的结果赋值给变量，求指教