Metadata

ID: php-best-practices/unset-loop-references

Language: PHP

Severity: Warning

Category: Error Prone

Description

This rule requires that all references created during loops, such as foreach, should be unset after the loop has completed. This is important because PHP handles variable scope differently than some other programming languages. In PHP, a reference set inside a foreach loop will continue to exist after the loop has finished, potentially leading to unexpected behavior.

If a reference is not unset after a loop, it can accidentally be used later in the code, causing bugs that are difficult to trace. In the non-compliant code sample, $value is a reference to each element of $arr in the loop. After the loop, $value is still a reference to the last element of $arr. If $value is modified, the last element of $arr is also modified, which is likely not the intended behavior.

To avoid this, always explicitly unset references after the loop with unset(). This good practice ensures that the reference does not persist beyond its intended scope, preventing potential bugs and making your code more robust and easier to understand. Following this rule will help you write cleaner, more predictable code and reduce the likelihood of encountering difficult-to-diagnose bugs.

Non-Compliant Code Examples

<?php
foreach ($arr as &$value) {
  $value += 10;
}
$value = 'x';

Compliant Code Examples

<?php
foreach ($arr as &$value) {
  $value += 10;
}
unset($value);
$value = 'x';

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