1.2.549. Immutable Signature

Overwrites makes refactoring a method signature difficult. PHP enforces compatible signature, by checking if arguments have the same type, reference and default values.

In PHP 7.3, typehint had to be the same, or dropped. In PHP 7.4, typehint may be contravariant (arguments), or covariant (returntype).

This analysis may be configured with maxOverwrite. By default, a minimum of 8 overwritten methods is considered difficult to update. When refactoring a method, all the related methodcall may have to be updated too. Adding a type, a default value, or a new argument with default value won’t affect the calls, but only the definitions. Otherwise, calls will also have to be updated.

IDE may help with signature refactoring, such as Refactoring code.

<?php

// Changing any of the four foo() method signature will trigger a PHP warning
class a {
    function foo($a) {}
}

class ab1 extends a {
    // four foo() methods have to be refactored at the same time!
    function foo($ab1) {}
}

class ab2 extends a {
    function foo($ab2) {}
}

class ab3 extends ab1 {
    function foo($abc1) {}
}

?>

Name

Default

Type

Description

maxOverwrite

8

integer

Minimal number of method overwrite to consider that any refactor on the method signature is now hard.

See also Covariance and contravariance (computer science) and extends.

1.2.549.2. Connex PHP features

1.2.549.2.1. Specs

Short name

Classes/ImmutableSignature

Rulesets

All, Appinfo, CE, Changed Behavior

Exakat since

1.9.9

PHP Version

All

Severity

Minor

Time To Fix

Quick (30 mins)

Precision

Very high

Available in

Entreprise Edition, Community Edition, Exakat Cloud