PHP The empty function reports an error solution

Fatal error: Can't use function return value in write context 'Fatal: Can't use function return value in write context: Can't use function return value write context

Take the following code for example:

<?php 
echo empty(strlen('test'));

Go to the PHP manual and see the following text in the empty function description:

Note :  empty()  only checks variables as anything else will result in a parse error. In other words, the following will not work: empty(trim($name)).

It is concluded that empty() only detects variables, and detecting anything that is not a variable will result in a parsing error!

Therefore, we cannot use empty to directly detect the value returned by the function. The solution is as follows:

<?php
$length = strlen('test');
echo empty($length);