Not All Strings In Arrays

<?php

class A {
    function __toString() {
        return "A";
    }
}

$a = new a;

$b = [$a => $a]; //Illegal offset type

print_r($b);

Array keys are coerced into strings or integers, while array values are left intact.

Yet, this doesn’t apply to array keys, so this code will display an Uncaught TypeError: Illegal offset type, even without strict_types.

This code needs an explicit cast to string to work.

See Also

• __toString() Magic Method

• string or not? [Try me]

PHP Features

• type-juggling

• string

• class

• cast

• array

Last updated: 14 July 2026