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group___data-_structures.html
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<hr/><a name="details" id="details"></a><h2>Overview</h2>
<p>For classic computer science data structures. </p>
<p>iOS provides most of the important data structures such as arrays, dictionaries, and sets. However, it is missing some lesser-used data structures such as linked lists. <a class="el" href="interface_nimbus.html" title="The Nimbus state interface.">Nimbus</a> makes use of the linked list data structure to provide an efficient, least-recently-used cache removal policy for its in-memory cache, <a class="el" href="interface_n_i_memory_cache.html" title="An in-memory cache for storing objects with expiration support.">NIMemoryCache</a>.</p>
<h2>Comparison of Data Structures</h2>
<pre>
Requirement | <a class="el" href="interface_n_i_linked_list.html" title="A singly linked list implementation.">NILinkedList</a> | NSArray | NSSet | NSDictionary
=====================================================================
Instant arbitrary | YES | NO | YES | YES
insertion/deletion | [1] | | |
---------------------------------------------------------------------
Consistent object | YES | YES | NO | NO
ordering | | | |
---------------------------------------------------------------------
Checking for object | NO | NO | YES | NO
existence quickly | | | |
---------------------------------------------------------------------
Instant object access | YES | NO | YES | YES
| [1] | | | [2]
---------------------------------------------------------------------</pre><ul>
<li>[1] Note that being able to instantly remove and access objects in an <a class="el" href="interface_n_i_linked_list.html" title="A singly linked list implementation.">NILinkedList</a> requires additional overhead of maintaining NILinkedListLocation objects in your code. If this is your only requirement, then it's likely simpler to use an NSSet. A linked list <em>is</em> worth using if you also need consistent ordering, seeing as neither NSSet nor NSDictionary provide this.</li>
<li>[2] This assumes you are accessing the object with its key.</li>
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<h2>Why <a class="el" href="interface_n_i_linked_list.html" title="A singly linked list implementation.">NILinkedList</a> was Built</h2>
<p><a class="el" href="interface_n_i_linked_list.html" title="A singly linked list implementation.">NILinkedList</a> was built to solve a specific need in Nimbus' in-memory caches of having a collection that guaranteed ordering, constant-time appending, and constant time removal of arbitrary objects. NSArray does not guarantee constant-time removal of objects, NSSet does not enforce ordering (though the new NSOrderedSet introduced in iOS 5 does), and NSDictionary also does not enforce ordering. </p>
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<tr><td class="mdescLeft"> </td><td class="mdescRight">A singly linked list implementation. <a href="interface_n_i_linked_list.html#details">More...</a><br/></td></tr>
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