Why You Should Always Use unset($value); After a foreach Loop in PHP

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Learn why using unset($value); after a foreach loop in PHP is essential to prevent unexpected behavior. Understand how references work and how to safely modify array elements with examples.

When you use &$value in a foreach loop, like this:

foreach ($arr as &$value) {
    $value = $value * 2;
}

PHP creates a reference to the array element, not a copy. After the loop ends, $value still points to the last element of the array.

That means if you use $value later in your code, you might accidentally change the last element of the array — even without realizing it.

⚠️ Example Without `unset($value);`

<?php
$arr = [1, 2, 3];

foreach ($arr as &$value) {
    // Doubles each element
    $value *= 2;
}

// Oops! This modifies the last element again!
$value = 99;

print_r($arr);
?>

Output:

Array
(
    [0] => 2
    [1] => 4
    [2] => 99  // ← unexpected!
)

✅ Example With `unset($value);`

<?php
$arr = [1, 2, 3];

foreach ($arr as &$value) {
    $value *= 2;
}
unset($value); // break the reference

$value = 99; // Now this does NOT affect $arr

print_r($arr);
?>

Output:

Array
(
    [0] => 2
    [1] => 4
    [2] => 6  // ← safe and expected
)

🔑 Summary:

Use unset($value); to break the lingering reference after a foreach loop with &.
This helps prevent accidental changes to your original array.