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POSimpleStocks protocol usage (Apple sample code)
 

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    <p>In the <a href="https://developer.apple.com/legacy/library/samplecode/SimpleStocks/Introduction/Intro.html" rel="nofollow">SimpleStocks</a> sample code provided by Apple, dataSource is defined as follows:</p> <pre><code>property (nonatomic, weak) IBOutlet id &lt;APLSimpleStockViewDataSource&gt; dataSource; </code></pre> <p>and then used variously as follows (only 2 examples, but there are more in the code)</p> <pre><code>NSInteger dataCount = [self.dataSource graphViewDailyTradeInfoCount:self]; NSArray *sortedMonths = [self.dataSource graphViewSortedMonths:self]; </code></pre> <p>I understand what graphViewDailyTradeInfoCount does, and also graphViewSortedMonths.I would have understood: <code>NSInteger dataCount = [APLStockViewController graphViewDailyTradeInfoCount:self];</code> (Tried that, and I think I know why that can't work)</p> <p>Here's the rub: The way I read the 1st line of code, dataSource is being sent the message graphViewDailyTradeInfoCount (which returns some numeric value specifying how many transactions occurred). If we assume 25 transactions, essentially [dataSource 25]; And now my mind is boggling, because I am strongly expecting that somewhere, there would be code telling dataSource what to do with the 25 it is being sent. But there isn't!!!</p> <p>Then the boggling increases by an order of magnitude: dataSource having been sent the 25, it now returns that and puts it into dataCount. How does it know to do that, there's no code anywhere that I can find for that either.</p> <p>And now, tickle me ballistic, in the second line of code, dataSource knows to accept (and then return) an NSArray.</p> <p>In my ever rarer sane moments, it looks to me like dataSource really doesn't do anything other than "pass through" stuff that it gets handed. Computers can't do magic, it feels like a feature, but where is it documented ?</p> <p>Thanks!</p>
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