Parameter Shadows Property

ID

php.parameter_shadows_property

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Php

Tags

naming, reliability

Description

Reports a method parameter whose name matches a property declared on the enclosing class. Inside the body an unqualified reference to that name resolves to the parameter, so the property can only be reached through $this→name.

Rationale

The shadow is silent: the code parses and runs, but every unqualified use of the name now refers to the parameter rather than the property. The bug surfaces the moment the author forgets the $this→ qualifier and unintentionally reads or writes the parameter where they meant the property — a mistake that survives refactoring poorly and is easy to miss in review. Renaming the parameter removes the ambiguity at the source.

<?php
class Counter {
    private int $count = 0;

    public function bump(int $count): int {   // FLAW — parameter shadows the property
        return $count + 1;                    // reads the parameter, not $this->count
    }

    public function bumpBy(int $delta): int {  // OK — distinct name, no ambiguity
        return $this->count + $delta;
    }
}

Remediation

Rename the parameter to a name distinct from every property of the enclosing class (for example a more specific or abbreviated form), so that unqualified references inside the method are unambiguous.

References