An indexer is something that takes an object and assigns a unique id to it. This id can normally fit into an array. It also handles the recycling of these ids. It will use an allocator and a deallocator for this purpose.
This is a queue implemented via a linked list
http://www.cs.usfca.edu/~galles/visualization/QueueLL.html
So one is a collection and the other isn't. The behavior between the two is different. The uses are different. Everything about them is different ^)^.
Now, if you were asking about an (I don't like this name, but this is what we call it here) indexed array, that is indeed a collection. An Indexed Array is nothing at all like an Indexer, the two have nothing to do with each other
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