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PO"Prefix" and "as" cast
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copied!<p>This seems to be a very stupid question about casting, but...</p> <p>I have the following setup:</p> <p>There are a number of classes derivces from a main class. At some point in time and space I get an item, and want to handle it as object of subclass.</p> <p>Asume:</p> <pre><code>class subClassA : mainclass class subClassB : mainclass </code></pre> <p>Now I have some if to ask which class it is:</p> <pre><code>if(someObject is subClassA) { subClassA aA = someObject as subClassA ; } </code></pre> <p>While for most subClasses the correct object is returned, I get for one subClass a <code>null</code>-Object.</p> <p>If I do the following:</p> <pre><code>if(someObject is subClassA) { subClassA aA = someObject as subClassA ; // <- aA = null; someObject is shown in debugger as object of subClassA object test = someObject as subClassA; // <- object is not null // or subClassA aB = (subClassA)someObject; // <- object is not null, shows the correct object } </code></pre> <p>I have results in <code>test</code> and <code>aB</code>.</p> <p>What I do not understand: </p> <p>Why does <code>as</code> fail and the prefix cast succeed?</p> <hr> <p>Now I'm completly lost. </p> <pre><code>if(someObject is subClassA) { subClassA aA = someObject as subClassA ; // <- aA = null; someObject is shown in debugger as object of subClassA subClassA aB = someObject as subClassA ; // <- aB != null. } if(someObject is subClassA) { subClassA aB = someObject as subClassA ; // <- aB != null. } </code></pre> <p>The name aA is localy defined. Only one thread accesses the method. If I just rename aA it works.</p>

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