Why can't I unset a variable in a `foreach` loop?

Question

Why can't I unset a variable in a foreach loop?

<?php

$array = array(a,s,d,f,g,h,j,k,l);

foreach($array as $i => $a){
 unset($array[1]);
 echo $a . "\n";
}

print_r($array);

In the code, the variable is in scope within the foreach loop, but outside the loop it's unset. Is it possible to unset it within the loop?

Answer 1

You need to pass the array by reference, like so:

foreach($array as $i => &$a){

Note the added &. This is also stated in the manual for foreach:

In order to be able to directly modify array elements within the loop precede $value with &. In that case the value will be assigned by reference.

This now produces:

a
d
f
g
h
j
k
l
Array
(
    [0] => a
    [2] => d
    [3] => f
    [4] => g
    [5] => h
    [6] => j
    [7] => k
    [8] => l
)