上面定义的回调函数未找到

Question

I have this code snippet that is supposed to find the differences between two arrays of feed items:

protected function execute()
{
    $existingFeedItems = $feed->getItems();
    $newFeedItems = $feed->loadItems();

    function compareFeedItemIds($feedItem1, $feedItem2)
    {
        return $feedItem1->getFeedItemId() == $feedItem2->getFeedItemId() ? 0 : -1;
    }

    $feedItemsAdded = array_udiff($newFeedItems, $existingFeedItems, "compareFeedItemIds");
    $feedItemsRemoved = array_udiff($existingFeedItems, $newFeedItems, "compareFeedItemIds");
    $unchangedFeedItems = array_uintersect($newFeedItems, $existingFeedItems, "compareFeedItemIds");
}

This will throw the error:

Warning: array_udiff() expects parameter 3 to be a valid callback, function 'compareFeedItemIds' not found or invalid function name

Even though I have defined that function above. What is the reason for PHP throwing this error? I have to add I am executing this from an object's method context.

Answer 1

If your callback function is defined within a namespace, then you need to indicate that namespace when you make the udiff() call.

$feedItemsAdded = array_udiff($newFeedItems, $existingFeedItems, "namespace\\compareFeedItemIds");

Otherwise PHP will search for the callback function in the global namespace