Compatibility¶

Compatibility refers to the ability of two or more things to work together without conflicts or issues.

In PHP context, it may refer to

version compatibility, when code works in both versions
system compatibility, when code works on different operating systems
method compatibility, when methods are compatible in the parent and the child class.

<?php

class X {
    function foo(int $i) {}
}

class Y extends X {
    // The type must be compatible with the one of the parent
    // The name does not have to be the same as in the parent
    function foo(int|null $b) {}
}

?>

Related : Method Compatibility, Interoperability, Migration