swoole_process a very strange problem

$str and $str1 are both arrays, one will report an error when called, and the other will not

<code><?php

$str[] = 'calback_func';
$str1 = ['calback_func'];

//$str[0] 改成 $str1[0] 就会报错
$process = new swoole_process($str[0]);

$pid = $process->start();

function calback_func(swoole_process $worker){// 第一个处理
   echo $worker->callback .PHP_EOL;
}</code>

#Error code

They are all characters, why is this happening....

Reply content:

$str and $str1 are both arrays, one will report an error when called, and the other will not

<code><?php

$str[] = 'calback_func';
$str1 = ['calback_func'];

//$str[0] 改成 $str1[0] 就会报错
$process = new swoole_process($str[0]);

$pid = $process->start();

function calback_func(swoole_process $worker){// 第一个处理
   echo $worker->callback .PHP_EOL;
}</code>

#Error code

They are all characters, why is this happening....