PHP - override function with different number of parameters

Question

I'm extending a class, but in some scenarios I'm overriding a method. Sometimes in 2 parameters, sometimes in 3, sometimes without parameters.

Unfortunately I'm getting a PHP warning.

My minimum verifiable example: http://pastebin.com/6MqUX9Ui

<?php

class first {
    public function something($param1) {
        return 'first-'.$param1;
    }
}

class second extends first {
    public function something($param1, $param2) {
        return 'second params=('.$param1.','.$param2.')';
    }
}

// Strict standards: Declaration of second::something() should be compatible with that of first::something() in /home/szymon/webs/wildcard/www/source/public/override.php on line 13

$myClass = new Second();
var_dump( $myClass->something(123,456) );

I'm getting PHP error/warning/info: error screen

How can I prevent errors like this?

You can't because it violates LSP http://en.wikipedia.org/wiki/Liskov_substitution_principle — Mike B, Apr 15 '13 at 13:57

score 42 · Answer 1 · answered Feb 13 '17 at 21:30

you can redefine methods easily adding new arguments, it's only needs that the new arguments are optional (have a default value in your signature). See below:

class Parent
{
    protected function test($var1) {
        echo($var1);
    }
}

class Child extends Parent
{
    protected function test($var1, $var2 = null) {
        echo($var1);
        echo($var1);
    }
}

For more detail, check out the link: http://php.net/manual/en/language.oop5.abstract.php

score 2 · Answer 2 · answered Apr 15 '13 at 14:03

2

Another solution (a bit "dirtier") is to declare your methods with no argument at all, and in your methods to use the func_get_args() function to retrieve your arguments...

http://www.php.net/manual/en/function.func-get-args.php

answered Apr 15 '13 at 14:03

Damien Legros

519
3
7

score -1 · Answer 3 · answered Apr 15 '13 at 13:59

Your interface/abstract class or the most parent class, should cotantin the maximum number of params a method could recieve, you can declare them explicitely to NULL, so if they are not given, no error will occur i.e.

Class A{
public function smth($param1, $param2='', $param3='')

Class B extends A {
public function smth($param1, $param2, $param3='')

Class C extends B {
public function smth($param1, $param2, $param3);

In this case, using the method smth() as an object of 'A' you will be obligated to use only one param ($param1), but using the same method as object 'B' you will be oblgiated to use 2 params ($param1, $param2) and instanciating it from C you have to give all the params

This is exactly the other way around. This script will lead to multiple warnings and errors as an object of type B does not behave like an object of type A which is a requirement. — fietserwin, Jun 18 '20 at 14:08

PHP - override function with different number of parameters

3 Answers3