Avoid Reassigning Parameters

ID

php.avoid_reassigning_parameters

Severity

info

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

Php

Tags

code_smell, reliability

Description

Reports a statement that rebinds a function parameter inside the body of the function that declares it — by plain assignment, compound assignment, or increment/decrement. By-reference parameters (&$p) are exempt, since rebinding them is exactly how they return a value to the caller.

Rationale

When a parameter is reassigned the body no longer matches the caller’s view of the call: the original argument value is silently lost partway through the function, debuggers and stack traces show a value the caller never passed, and a later reader has to scan the whole body to learn what the name currently holds. Copying the argument into a clearly named local keeps the parameter intact and makes the transformation explicit.

<?php
function normalize($name) {
    $name = trim($name);          // FLAW — the original argument is now unrecoverable
    return strtolower($name);
}

function normalize($name) {
    $clean = trim($name);         // OK — original parameter preserved, intent explicit
    return strtolower($clean);
}

Remediation

Introduce a local variable initialised from the parameter and operate on the local. Leave the parameter untouched so the original argument value remains available throughout the function.

References