StackOverflow2013

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copied!<p><em>I'm able to work the examples, but he doesn't explain exactly why he's using a class in that way (NSNumber instead of int or double for example)...</em></p> <p><em>There are some things that just don't make sense with Obj-C and Cocoa, why can't I put integers into an NSMutableArray?</em></p> <p><a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/nsnumber_Class/Reference/Reference.html#//apple_ref/doc/uid/20000178-3041" rel="noreferrer"><code>NSNumber</code></a> is a much more useful type than a primitive type like <code>int</code> or <code>double</code>, as it is often used in conjunction with other objects you'll run into as you program in Cocoa.</p> <p>For example, in order to package a number as a value into a resizable array (like an <code>NSMutableArray</code>) or an associative array (an instance of <a href="http://developer.apple.com/DOCUMENTATION/Cocoa/Reference/Foundation/Classes/NSDictionary_Class/Reference/Reference.html#//apple_ref/doc/uid/20000140-9552" rel="noreferrer"><code>NSDictionary</code></a>), you need to turn the number primitive (<code>int</code>, <code>double</code>, etc.) into a <a href="http://developer.apple.com/documentation/Cocoa/Conceptual/Archiving/Archiving.html" rel="noreferrer">serializable</a>, or archivable object — an <code>NSNumber</code>. </p> <p>Primitives can't be serialized, unlike an <code>NSNumber</code>, because primitives aren't in the basic set of "Core Foundation" types (<code>NSNumber</code>, <code>NSArray</code>, <code>NSString</code>, etc.) that Apple has worked hard to make available to you. </p> <p>Also, by using <code>NSNumber</code> you also get a lot of bonus convenience methods for free: you can quickly convert the number into a string, for example, by simply typing <code>[myNumber stringValue]</code>.</p> <p>Or, if you're treating your <code>NSNumber</code> as the price of something ("$1.23"), you can apply an <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSNumberFormatter_Class/Reference/Reference.html#//apple_ref/doc/uid/20000202-9197" rel="noreferrer"><code>NSNumberFormatter</code></a> to make sure that operations on the number give results that have the format that you would expect (e.g. if you add two price values, you would expect to get a currency value in return).</p> <p>That's not to say you can't or shouldn't use <code>int</code> or <code>double</code> variables. But in many cases, you'll find an <code>NSNumber</code> is a better option, in that you can write less code and get a lot of functionality for "free".</p>

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