Unexpected behavior in foreach when looping and disconnecting in ArrayObject. The item is ignored.

Question

( examples below! )

we just upgraded our server to PHP7 and after that we found an error in our code related to ArrayObject.

The code simply iterates over a copy of the object (type native ArrayObject). The foreach identifier iterates by value.

The purpose of the code is to filter out some values ​​that you do not need. In the example, if the iterated value is two or three, disable it. I tried this using an iterator instead of the copied value and without an iterator.

Results:

- Iterator

• PHP 5.6: works as expected, the return value is an array with no two or three
• PHP 7: it only removes “two” and it seems that an element with a value of “three” is not evaluated (see the echo inside the loop, it does not print “three”)

- No iterator

• PHP 5.6: receives a notification, but works as expected, the return value is an array with no two or three
• PHP 7: it only removes “two” and it seems that an element with a value of “three” is not evaluated (see the echo inside the loop, it does not print “three”)

First loop => $ key = 0, $ value = "one" // continue

Second loop => $ key = 1, $ value = "second" // unset

Third loop => $ key = 3, $ value = "four" // WTF? where $ key = 2, $ value = "three" ????

Therefore, I cannot understand what is happening. Our temporary solution is to iterate over the original object and not use it. Does anyone know what changes in the PHP core (or ArrayObject / ArrayIterator) do this? I have a search on this, but some people have this problem with foreach if the element was repeated by reference.

If you switch between PHP 5.6 and 7, the behavior changes.

Example 1 (with an iterator)

$elements = new ArrayObject(); $elements->append('one'); $elements->append('two'); $elements->append('three'); $elements->append('four'); print_r($elements); $clone = clone $elements; $it = $clone->getIterator(); echo "\n------\n"; foreach ($it as $key => $value) { echo $key."\t=>\t".$value."\n"; if ($value == 'two' || $value == 'three') { $it->offsetUnset($key); } } echo "\n------\n"; print_r($clone); 

Example 2 (without an iterator)

 $elements = new ArrayObject(); $elements->append('one'); $elements->append('two'); $elements->append('three'); $elements->append('four'); print_r($elements); $clone = clone $elements; echo "\n------\n"; foreach ($clone as $key => $value) { echo $key."\t=>\t".$value."\n"; if ($value == 'two' || $value == 'three') { $clone->offsetUnset($key); } } echo "\n------\n"; print_r($clone); 

Many thanks!

Answer 1

From my point of view, it is considered bad practice to change the array when passing through it, and the correct way to do this would be to use array_filter .

Since you have an ArrayObject , one solution would be to export it to an array, filter it with array_filter and create a new ArrayObject from the filtered array.

See also here: ArrayObject Filter (PHP)

This behavior is probably due to the fact that php7 handles it differently. As mentioned here: http://php.net/manual/en/control-structures.foreach.php in php5 foreach uses an internal array pointer as opposed to php7.