Named Parameter Inheritance

<?php
  
interface I { function foo(int $i); }

class X implements I { function foo(int $x) { echo $x; } }

(new X)->foo(x: 1);
(new X)->foo(i: 1);
  
?>

PHP enforces the methods compatibility with their types, names, and various options, but not with the parameter names. This means the parameter name existence is enforced, but the name might change. It might change between the parent and the child, but also, between the class and the interface.

It is recommended to keep all these parameter’s name identical, so as to keep consistence in the code, and simplify the usage of the method, with named parameters.

See Also

• Function parameters and arguments (PHP manual)
• named parameter changes [Try me]

PHP Error Messages

• Unknown named parameter $%s

PHP Features

• bug
• parameter
• named-parameter
• inheritance

Last updated: 10 September 2026