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POconvincing C# compiler that execution will stop after a member returns
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copied!<p>I don't think this is currently possible or if it's even a good idea, but it's something I was thinking about just now. I use MSTest for unit testing my C# project. In one of my tests, I do the following:</p> <pre><code>MyClass instance; try { instance = getValue(); } catch (MyException ex) { Assert.Fail("Caught MyException"); } instance.doStuff(); // Use of unassigned local variable 'instance' </code></pre> <p>To make this code compile, I have to assign a value to <code>instance</code> either at its declaration or in the <code>catch</code> block. I could alternatively <code>return</code> after the <code>Assert.Fail</code> but that's still a workaround instead of the compiler just <em>knowing</em> that execution cannot continue after this point. <code>Assert.Fail</code> will never, to the best of my knowledge, allow execution to proceed past it, hence <code>instance</code> will never be used without a value. Why is it then that I must assign a value to it? If I change the <code>Assert.Fail</code> to something like <code>throw ex</code>, the code compiles fine, I assume because it knows that exception will disallow execution to proceed to a point where <code>instance</code> would be used uninitialized.</p> <p>Contrariwise, what if I didn't want the test to fail, but rather be marked as inconclusive? I could do an <code>Assert.Inconclusive</code> instead of <code>Fail</code>, and it would be nice if the compiler knew execution would not continue after that.</p> <p>So is it a case of runtime versus compile-time knowledge about where execution will be allowed to proceed? Would it ever be reasonable for C# to have some way of saying that a member, in this case <code>Assert.Fail</code>, will never allow execution after it returns? Maybe that could be in the form of a method attribute. Would this be useful or an unnecessary complexity for the compiler?</p> <p><strong>Outside Unit Tests</strong></p> <p>Since people are [validly] pointing out that this is a silly way to write a unit test, consider my question outside the realm of unit testing:</p> <pre><code>MyClass instance; if (badThings) { someMethodThatWillNeverReturn(); } else { instance = new MyClass(); } instance.doStuff(); </code></pre> <p>Here potentially I could replace the call to <code>someMethodThatWillNeverReturn</code> with throwing an exception, and perhaps if I had stuff to do, I could do it in the constructor for the exception.</p> <p><strong>Resharper Knows</strong></p> <p>If I add a <code>return</code> after <code>Assert.Fail</code> or <code>Assert.Inconclusive</code>, Resharper colors <code>return</code> gray and has a tooltip saying "Code is heuristically unreachable."</p>

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