1.2.1224. Type Dodging

It is always possible to rewrite a parameter type by using union types. When the parent class or interface requires a type, the child class may create a union type with the required type, add a secondary type and ignore the first one.

This is part of the Liskov Substitution Principle, so the syntax is legit. When the union type is only used to circumvent the previous typing, it is now a violation, as such a typed data would be valid, but ignored.

<?php

interface i {
     function foo(A $a) {}
}

class x implement i {
     function foo(A | string $a) {
             if ($a instanceof A) {
                     throw new Exception('Unused type.');
             }
             // ...
     }
}
?>

1.2.1224.1. Suggestions

• Avoid using union type to enlarge types in parameters

1.2.1224.2. Specs

Short name	Functions/TypeDodging
Rulesets	All, Changed Behavior, Class Review
Exakat since	2.5.0
Severity	Minor
Time To Fix	Quick (30 mins)
Precision	Medium
Features	liskov
Available in	Entreprise Edition, Exakat Cloud