Hi,<br><br>I trying to implement Andrei&#39;s Expected&lt;T&gt; from his &quot;Systematic Error Handling in C++&quot; talk<div>(<a href="http://channel9.msdn.com/Shows/Going+Deep/C-and-Beyond-2012-Andrei-Alexandrescu-Systematic-Error-Handling-in-C">http://channel9.msdn.com/Shows/Going+Deep/C-and-Beyond-2012-Andrei-Alexandrescu-Systematic-Error-Handling-in-C</a>) in C++03 / BOOST<br>
</div><div><br></div><div>In short: Expected&lt;T&gt; holds either T or exception_ptr holding exception that prevented T&#39;s creation. Think of single threaded future&lt;T&gt;.</div><div><br></div><div>One of main purposes of this type is efficiency - code that computes T would normally throw in case of errors but instead it returns exception by value which causes Expected&lt;T&gt; to be initiated with exception type instead of actual value of T. Important part is that no throwing happens in library code (making it fast).</div>
<div><br></div><div>As with future&lt;T&gt; throwing of stored exception only happens upon client&#39;s request - a call to get() in case of invalid computation (Expected&lt;T&gt;::valid() may be called beforehand to check if computation succeeded).</div>
<div><br></div><div>To the point: Andrei&#39;s code uses std::make_exception_ptr() which I assume is std version of boost::copy_exception(). Now problem with copy_exception() is that it actually throws! So the whole idea of not throwing is gone by the fact that I don&#39;t know how to transform (const Exception&amp;) into boost::exception_ptr (without throwing via copy_exception()).</div>
<div><br></div><div>How does std::make_exception_ptr() work (as I assume it does not throw &amp; return current_exception() as boost::copy_exception does)? Any suggestions welcome.</div><div><br></div><div><br></div><div>
Cheers.</div><div><div>Szymon Gatner<br><br>
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