TYPO3 Core

Claus shared some thoughts regarding this issue on slack, I quote it here:

this can probably be explained by pointers and Iterator, combined with not cloning the iterator and using foreach() to determine which object you reference when you use `0` as index in an ObjectStorage

logic flow would be: 1) you start iterating outside, 2) you try to access the property with numeric index, 3) ObjectAccess::getPropertyPath does iteration of your ObjectStorage to find the member, 4) pointer is left at the end of the ObjectStorage(Iterator) and the loop terminates early.

this would probably also have been worse if the pointer was actually reset after iteration (there are several threads about this problem. TL;DR pointer reset works one way for arrays and another for Iterators)

the reason you don't see it when using VHS iterator is you avoid the outer iteration and instead access each member directly (causing a foreach($objectStorage) on each access, but resulting in a working loop)

if that's right then fixing it becomes a pretty complicated issue

you might be tempted to use iterator_to_array($objectStorage)[$index] but that wouldn't really be efficient

you might also be tempted to `clone $objectStorage` in ObjectAccess but that could easily cause unwanted side effects for objects defining `__clone`

my straight-forward recommendation would be to be aware of this pointer thing and design your code accordingly. It would also apply if you attempt the same procedure in PHP directly.

To give some more information: Claus is right. The same ObjectStorageObject is iterated inside its first iteration again, thus exiting the first (outer) loop after the first iteration. The same thing happens obviously if you write the following:

$objectStorage = $object->getObjectStorageProperty();
foreach ($objectStorage as $object) {
  // This would be the loop of the f:for ViewHelper
  echo 'outer loop';
  foreach ($objectStorage as $object) {
    // This would be the loop of in ObjectAccess to find the property value
    echo 'inner loop';
  }
}

This will give you only one 'outer loop'. Suggested solution is to clone the $objectStorage within the objectAccess class (where the second loop happens) which was tested successfully but not pushed yet, due to possible sideffects. It would also be possible to clone the $objectStorage before the loop in the f:for ViewHelper but this might lead to even more unwanted sideeffects.

A workaround for now is to convert the objectStorage to an array ($objectStorage->toArray()) before passing it to f:for ViewHelper.

Issue was introduced here: #66995

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/53525

Patch set 3 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/53525

Patch set 1 for branch TYPO3_8-7 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/53533