Data-Structures.html

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<div class="title">Data Structures<div class="ingroups"><a class="el" href="NimbusCore.html">Nimbus Core</a></div></div>  </div>
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Classes</h2></td></tr>
<tr class="memitem:"><td class="memItemLeft" align="right" valign="top">class &#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="NILinkedList.html">NILinkedList</a></td></tr>
<tr class="memdesc:"><td class="mdescLeft">&#160;</td><td class="mdescRight">A singly linked list implementation.  <a href="NILinkedList.html#details">More...</a><br/></td></tr>
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<a name="details" id="details"></a><h2 class="groupheader">Overview</h2>
<p>For classic computer science data structures. </p>
<p><a class="el" href="NILinkedList.html" title="A singly linked list implementation. ">NILinkedList</a> has been deprecated and will soon be removed altogether. Use NSMutableOrderedSet instead.</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. Nimbus 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="NIMemoryCache.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="NILinkedList.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 a <a class="el" href="NILinkedList.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>
</ul>
<h2>Why <a class="el" href="NILinkedList.html" title="A singly linked list implementation. ">NILinkedList</a> was Built</h2>
<p><a class="el" href="NILinkedList.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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