StackOverflow2013

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POWhy in Objective-C does doing alloc and init in separate statements cause the object to be released according to the Xcode static analyzer?
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copied!<p>I'm making my first steps with Objective-C and have encountered a minor, albeit confusing issue with the static analyzer (Product->Analyze) in XCode 4.1. I have created a simple Fraction class for rational numbers which I allocate and initialize like this,</p> <pre><code>Fraction* f = [[[ Fraction alloc ] initWithNumerator:3 withDenomimator:5] autorelease]; [ f print ]; </code></pre> <p>where <code>print</code> is a method which just uses <code>NSLog</code> to display the fraction, everything works fine. However, if I split the <code>alloc</code>/<code>init</code> construct apart into two statements (I realize this is non-idiomatic - I'm just trying to understand the machinery) and use manual <code>release</code> rather than <code>autorelease</code> giving:</p> <pre><code>Fraction* f = [ Fraction alloc ]; // 1. Method returns an Objective-C object with // a +1 retain count (owning reference) [ f initWithNumerator:3 withDenomimator:5]; // 2. Object released [ f print ]; // 3. Reference-counted object is used after it is released [ f release ]; </code></pre> <p>the program still appears to run without error, but the XCode analyzer gives the warnings in the comments. Why does XCode think the <code>init</code> call causes the object to be released?</p> <p>Thinking through this further as I frame the question I can see that my two programs are not quite equivalent because in the first snippet my pointer <code>f</code> is the result of the call to <code>init</code> whereas in the second snippet it is the result of <code>alloc</code>. So changing my code to,</p> <pre><code> Fraction* a = [ Fraction alloc ]; Fraction* f = [ a initWithNumerator:3 withDenomimator:5]; [ f print ]; [ f release ]; // or should it be [ a release ] ? </code></pre> <p>makes it exactly equivalent and the static analyzer stops complaining. So is it possible that <code>init</code> can return a different pointer than the one passed to it from <code>alloc</code>, rather than just <em>configuring</em> the memory it has been passed? With this code should I pair <code>[ a release ]</code> with the <code>alloc</code> or <code>[ f release ]</code> with the <code>init</code>?</p>

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