Inconsistent Constructor Signatures

<?php

declare(strict_types=1);

class x {
    function __toString() : string {
        return "YES";
    }
}

function foo(string $a) {}

// piece of syntax of the day (POSOTD)
echo $x = new x;

print " A $x";

// Fata error: Argument #1 ($a) must be of type string, x given, foo($x);

?>

PHP enforces that methods have the same signature in a parent class and in a children class. It raises a Fatal Error if not.

Unless for constructors, where the signatures can be different.

This exception to the rule is for legacy purposes, as many source code have varying signatures in a class hierarchy.

Yet, modern OOP recommends to synchronize those signatures, so has to allow instantiation using the same set of arguments.

See Also

• Constructors and Destructors (PHP manual)

• Inconsistent Constructor Signatures [Try me]

PHP Features

• php

• class

• oop

Last updated: 14 July 2026