Promoted Properties Compatibility

<?php

interface i {
    // no promoted property
    function __construct(int $a);
}

class x implements i {
    // promoted property
    function __construct(private int $a) {}
}

class y extends x {
    // valid extension of a promoted property
    function __construct(int $a) {}
}

?>

Promoted properties are defined in a constructor signature. They cannot be defined in an abstract method, so they are not allowed in an abstract constructor: this is true in an abstract class and in an interface.

On the other hand, it is allowed to extend promoted properties without the promotion, and vice versa.

See Also

• Class Abstract (PHP manual)

• Promoting and compatibility [Try me]

PHP Features

• abstract

• property

• constructor

Last updated: 14 July 2026