Battle Of Definition¶

<?php

interface I {
    function __construct(int $i);
}

class X implements I {
    function __construct(int $i) {}
}

// Fatal error: Declaration of Yy::__construct(string $a) must be
// compatible with I::__construct(int $i)

class Y extends X {
    function __construct(string $a) {}
}

?>

Methods signatures must be compatible with the parent class’s definition. This is true, except for __construct(), for which the compatibility is never checked.

Yet, compatibility is still enforced when the __construct() definition is in an interface. Then, both the implementing table and all its children must have the interface’s compatibility.

See Also¶

Battle of definitions [Try me]
3v4l : __construct() signature enforced when in an interface [Try me]

PHP Features¶

Last updated: 14 July 2026