PHP snippet to highlight an array cursor being modified from outside an object or a class

foreach_is_modifying_array_cursor_from_outside.php

<?php

/**
 * Snippet to highlight an array cursor being modified from outside an object or
 * a class
 **/

class MyClass
{
    protected $arr = [];
    protected static $arrStatic = [];
    
    function __construct($array = []) {
        $this->arr = $array;
        self::$arrStatic = $array;
    }
    
    function getArr() {             return $this->arr;                      }
    
    function getArrStatic() {       return self::$arrStatic;                }
    
    function getCurrent() {         return current($this->arr);             }
    
    function getCurrentStatic() {   return current(self::$arrStatic);       }
}

echo 'phpversion() = ' . phpversion() . PHP_EOL . PHP_EOL;

$o = new MyClass([1, 2, 3]);

echo '__Instance: initial state__' . PHP_EOL;
echo 'MyClass::getCurrent() = '; var_dump($o->getCurrent());
echo 'current(MyClass::getArr()) = '; var_dump(current($o->getArr()));
$a = $o->getArr();
echo 'current($a) = '; var_dump(current($a));

echo '$a = ';
print_r($a);

echo 'MyClass::getCurrent() = '; var_dump($o->getCurrent());
echo 'current(MyClass::getArr()) = '; var_dump(current($o->getArr()));
echo 'current($a) = '; var_dump(current($a));
unset($a);

echo PHP_EOL;
echo '__foreach with accessor__' . PHP_EOL;

foreach ($o->getArr() as $item) {
    echo $item . ' ';
}
echo PHP_EOL;

echo 'MyClass::getCurrent() = '; var_dump($o->getCurrent());
echo 'current(MyClass::getArr()) = '; var_dump(current($o->getArr()));

echo PHP_EOL;
echo '__foreach with local var__' . PHP_EOL;

$a = $o->getArr();
foreach ($a as $item) {
    echo $item . ' ';
}
echo PHP_EOL;

echo 'MyClass::getCurrent() = '; var_dump($o->getCurrent());
echo 'current(MyClass::getArr()) = '; var_dump(current($o->getArr()));
echo 'current($a) = '; var_dump(current($a));


echo '------------------------------------' . PHP_EOL;


echo '__Static: initial state__' . PHP_EOL;
echo 'MyClass::getCurrentStatic() = '; var_dump($o->getCurrentStatic());
echo 'current(MyClass::getArrStatic()) = '; var_dump(current($o->getArrStatic()));
$as = $o->getArrStatic();
echo 'current($as) = '; var_dump(current($as));

echo '$as = ';
print_r($as);

echo 'MyClass::getCurrentStatic() = '; var_dump($o->getCurrentStatic());
echo 'current(MyClass::getArrStatic()) = '; var_dump(current($o->getArrStatic()));
echo 'current($as) = '; var_dump(current($as));
unset($as);

echo PHP_EOL;
echo '__foreach with accessor__' . PHP_EOL;

foreach ($o->getArrStatic() as $item) {
    echo $item . ' ';
}
echo PHP_EOL;

echo 'MyClass::getCurrentStatic() = '; var_dump($o->getCurrentStatic());
echo 'current(MyClass::getArrStatic()) = '; var_dump(current($o->getArrStatic()));

echo PHP_EOL;
echo '__foreach with local var__' . PHP_EOL;

$as = $o->getArrStatic();
foreach ($as as $item) {
    echo $item . ' ';
}
echo PHP_EOL;

echo 'MyClass::getCurrentStatic() = '; var_dump($o->getCurrentStatic());
echo 'current(MyClass::getArrStatic()) = '; var_dump(current($o->getArrStatic()));
echo 'current($as) = '; var_dump(current($as));

output

phpversion() = 5.5.9-1ubuntu4.11

__Instance: initial state__
MyClass::getCurrent() = int(1)
current(MyClass::getArr()) = int(1)
current($a) = int(1)
$a = Array
(
    [0] => 1
    [1] => 2
    [2] => 3
)
MyClass::getCurrent() = int(1)
current(MyClass::getArr()) = int(1)
current($a) = int(1)

__foreach with accessor__
1 2 3 
MyClass::getCurrent() = bool(false)
current(MyClass::getArr()) = int(1)

__foreach with local var__
1 2 3 
MyClass::getCurrent() = int(1)
current(MyClass::getArr()) = int(1)
current($a) = bool(false)
------------------------------------
__Static: initial state__
MyClass::getCurrentStatic() = int(1)
current(MyClass::getArrStatic()) = int(1)
current($as) = int(1)
$as = Array
(
    [0] => 1
    [1] => 2
    [2] => 3
)
MyClass::getCurrentStatic() = int(1)
current(MyClass::getArrStatic()) = int(1)
current($as) = int(1)

__foreach with accessor__
1 2 3 
MyClass::getCurrentStatic() = bool(false)
current(MyClass::getArrStatic()) = int(1)

__foreach with local var__
1 2 3 
MyClass::getCurrentStatic() = int(1)
current(MyClass::getArrStatic()) = int(1)
current($as) = bool(false)

Lines 19 and 44 shows that foreach() moved the returned-array's cursor (it is now beyond the end of the elements).

It turns out to be an "issue" the PHP RFC: Fix "foreach" behavior is trying to fix. When using foreach, the internal pointer is altered.

(Thanks @pmartin)