1.2.567. Incompatible Signature Methods With Covariance

Methods should have the compatible signature when being overwritten.

The same signatures means the children class must have :

  • the same name

  • the same visibility or less restrictive

  • the same contravariant typehint or removed

  • the same covariant return typehint or removed

  • the same default value or removed

  • a reference like its parent

This problem emits a fatal error, for abstract methods, or a warning error, for normal methods. Yet, it is difficult to lint, because classes are often stored in different files. As such, PHP do lint each file independently, as unknown parent classes are not checked if not present. Yet, when executing the code, PHP lint the actual code and may encounter a fatal error.

<?php

class a {
    public function foo($a = 1) {}
}

class ab extends a {
    // foo is overloaded and now includes a default value for $a
    public function foo($a) {}
}

?>

See also Object Inheritance, PHP RFC: Covariant Returns and Contravariant Parameters and Incompatible Signature Methods.

1.2.567.2. Connex PHP features

1.2.567.2.1. Suggestions

  • Make signatures compatible again

1.2.567.2.2. Specs

Short name

Classes/IncompatibleSignature74

Rulesets

All, Analyze, Changed Behavior

Exakat since

1.3.3

PHP Version

With PHP 7.4 and more recent

Severity

Critical

Time To Fix

Quick (30 mins)

Precision

Medium

Examples

SuiteCrm

Available in

Entreprise Edition, Exakat Cloud