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POHow would you use Alexandrescu's Expected<T> with void functions?
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  1. POHow would you use Alexandrescu's Expected<T> with void functions?
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    copied!<p>So I ran across this (IMHO) very nice idea of using a composite structure of a return value and an exception - <code>Expected&lt;T&gt;</code>. It overcomes many shortcomings of the traditional methods of error handling (exceptions, error codes).</p> <p>See the <a href="http://channel9.msdn.com/Shows/Going+Deep/C-and-Beyond-2012-Andrei-Alexandrescu-Systematic-Error-Handling-in-C" rel="noreferrer">Andrei Alexandrescu's talk (Systematic Error Handling in C++)</a> and <a href="https://skydrive.live.com/?cid=f1b8ff18a2aec5c5&amp;id=F1B8FF18A2AEC5C5!1158" rel="noreferrer">its slides</a>.</p> <p>The exceptions and error codes have basically the same usage scenarios with functions that return something and the ones that don't. <code>Expected&lt;T&gt;</code>, on the other hand, seems to be targeted only at functions that return values.</p> <p>So, my questions are:</p> <ul> <li>Have any of you tried <code>Expected&lt;T&gt;</code> in practice?</li> <li>How would you apply this idiom to functions returning nothing (that is, void functions)?</li> </ul> <p><strong>Update:</strong></p> <p>I guess I should clarify my question. The <code>Expected&lt;void&gt;</code> specialization makes sense, but I'm more interested in how it would be used - the consistent usage idiom. The implementation itself is secondary (and easy).</p> <p>For example, Alexandrescu gives this example (a bit edited):</p> <pre><code>string s = readline(); auto x = parseInt(s).get(); // throw on error auto y = parseInt(s); // won’t throw if (!y.valid()) { // ... } </code></pre> <p>This code is "clean" in a way that it just flows naturally. We need the value - we get it. However, with <code>expected&lt;void&gt;</code> one would have to capture the returned variable and perform some operation on it (like <code>.throwIfError()</code> or something), which is not as elegant. And obviously, <code>.get()</code> doesn't make sense with void.</p> <p>So, what would your code look like if you had another function, say <code>toUpper(s)</code>, which modifies the string in-place and has no return value?</p>
 

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