PHP Bug or my misunderstanding of the language? [duplicate]

Question

This is the code that I don't understand (as the output).

<?php
$x = ['test1', 'test2', 'test3', 'test4'];
echo "First FOREACH\n";
foreach ($x as &$y)
{
    echo $y."\n";
}
echo "\n\nSecond FOREACH\n";
foreach ($x as $y)
{
    echo $y."\n";
}

?>

Output:

First FOREACH
test1
test2
test3
test4

Second FOREACH
test1
test2
test3
test3

PS: I'm running it under:

php -v
PHP 5.6.11-1ubuntu3.1 (cli) 
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2015 Zend Technologies
    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2015, by Zend Technologies

Answer 1

After the first foreach statement you have $y pointing to the last array item:

$x = ['test1', 'test2', 'test3', 'test4'];
$y =& $x[3];

Whenever you assign a value to $y original array will be modified.

When second foreach begins, on every iteration next value from $x is put into $y. So on every iteration original array will look like:

// first iteration
$x = ['test1', 'test2', 'test3', 'test1'];
// second iteration
$x = ['test1', 'test2', 'test3', 'test2'];
// third iteration
$x = ['test1', 'test2', 'test3', 'test3'];
// fourth iteration
$x = ['test1', 'test2', 'test3', 'test3'];

Answer 2

It's more of a feature, it's documented in the foreach manpage

Warning Reference of a $value and the last array element remain even after the foreach loop. It is recommended to destroy it by unset().

There are some relevant comments on the manpage, here's one of them http://php.net/manual/en/control-structures.foreach.php#111688

More info on how this happens here http://schlueters.de/blog/archives/141-References-and-foreach.html