SplDoublyLinkedList::shift

One may expect SplDoublyLinkedList::shift to properly maintain internal pointers, but this is not the case, this will yield no results, even if you rewind first<?phpwhile ($splDoublyLinkedList->valid()) {    yield $splDoublyLinkedList->shift();}?>It could be by design, but the following raises some more questions :<?php$test = new \SplDoublyLinkedList;$dataSet = [    ['id' => 1],    ['id' => 2],    ['id' => 3],    ['id' => 4],];foreach ($dataSet as $row) {    $test->push($row);}echo "count: " . $test->count() . PHP_EOL;echo "valid: " . ($test->valid() ? 'true' : 'false') . PHP_EOL;echo "current: " . var_export($test->current(), true) . PHP_EOL;echo "key: " . $test->key() . PHP_EOL;echo "1st shift: " . var_export($test->shift(), true) . PHP_EOL;echo "count: " . $test->count() . PHP_EOL;echo "valid: " . ($test->valid() ? 'true' : 'false') . PHP_EOL;echo "current: " . var_export($test->current(), true) . PHP_EOL;echo "key: " . $test->key() . PHP_EOL;echo "2nd shift: " . var_export($test->shift(), true) . PHP_EOL;echo "count: " . $test->count() . PHP_EOL;echo "valid: " . ($test->valid() ? 'true' : 'false') . PHP_EOL;echo "current: " . var_export($test->current(), true) . PHP_EOL;echo "key: " . $test->key() . PHP_EOL;echo "rewinding... " . PHP_EOL;$test->rewind();echo "current: " . var_export($test->current(), true) . PHP_EOL;echo "2nd shift: " . var_export($test->shift(), true) . PHP_EOL;echo "count: " . $test->count() . PHP_EOL;echo "valid: " . ($test->valid() ? 'true' : 'false') . PHP_EOL;echo "current: " . var_export($test->current(), true) . PHP_EOL;echo "key: " . $test->key() . PHP_EOL;?>will result in :<?php/*count: 4                valid: false                       <== First thing to note, you have no valid pointer unless you rewind firstcurrent: NULL                  <== hence no currentkey: 0                                <== but we have a valid keyoffsetGet(key): array (    <== indeed  'id' => 1,            )                       1st shift: array (               <== and shift does return first row  'id' => 1,            )                       count: 3                            <== and count is maintained as expectedvalid: false                      <== but internal pointer was left outside valid rangecurrent: NULL                 <== hence no current againkey: 0                                <== but we still have a valid keyoffsetGet(key): array (   <== indeed  'id' => 2,            )                       2nd shift: array (             <== and shift does return first row  'id' => 2,            )                       count: 2                           <== and count is maintained as expectedvalid: false                      <== still not valid etc ..current: NULL           key: 0                  offsetGet(key): array (   'id' => 3,            )                       rewinding...                    <== now rewindcurrent: array (             <== yay a current  'id' => 3,            )                       3rd shift: array (            <== shift ok  'id' => 3,            )                       count: 1                          <== count okvalid: true                     <== ouch valid current: NULL               <== with no currentkey: 0                              <== still our key is valid :ooffsetGet(key): array (   'id' => 4,            )                            */?>Conclusion : I may be missing something about why SplDoublyLinkedList::shift is not maintaining proper internal index in the first place, but I find it even more confusing to be able to end up with a valid valid() and a valid key() and no current() while there is obviously one.Tested on php 5.6.30 & 7.1.2 with the exact same result.