PHP – Foreach By Reference

Today I was writing some code in which I wanted to modify the values of an array within a for-loop. The obvious solution would be to use the key to modify the value but there is actually another way of doing it:

$arr = array(1,2,3,4,5);
foreach ($arr as &$value) {
  $value = $value * $value;
}
print_r($arr);

The above code will actually go through the array of integers 1 to 5 and change the array to be the squares of those values. The output is as follows:

Array
(
    [0] => 1
    [1] => 4
    [2] => 9
    [3] => 16
    [4] => 25
)

This works because placing the ampersand in front of the $value makes the variable refer to the actual value within the array and updating it will update the value within the array.

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