__sleep() Method Enforces Return Type

__sleep is a magic method that lists the name of the variables to serialize. It should come as an array, and is enforced as such since PHP 8.0.

PHP code

<?php

class x {
     function __sleep() {
             return 3;
     }
}

serialize(new x);

?>

Before

PHP Notice:  serialize(): __sleep should return an array only containing the names of instance-variables to serialize in /codes/nonArrayWithSleep.php on line 9

Notice: serialize(): __sleep should return an array only containing the names of instance-variables to serialize in /codes/nonArrayWithSleep.php on line 9

After

PHP Warning:  serialize(): x::__sleep() should return an array only containing the names of instance-variables to serialize in /codes/nonArrayWithSleep.php on line 9

Warning: serialize(): x::__sleep() should return an array only containing the names of instance-variables to serialize in /codes/nonArrayWithSleep.php on line 9

PHP version change

This behavior changed in 8.0

Error Messages

• serialize(): __sleep should return an array only containing the names of instance-variables to serialize