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copied!<p>There seem to be several issues with your code, one of which looks like a VS10 bug.</p> <ol> <li>You're calling <code>T::func()</code> from <code>A</code> without casting <code>A</code> to <code>T</code>, this is needed as part of CRTP since <code>A</code> doesn't derive from <code>T</code>. -- FixL <code>return static_cast<T*>(this)->func();</code></li> <li>What you're passing to <code>decltype</code> looks like a static function invocation while <code>func</code> is in fact an instance function. Since <code>decltype</code> <strong>doesn't</strong> actually run the function you should do something like this <code>decltype(static_cast<T*>(nullptr)->func())</code></li> <li><code>func</code> is private in <code>B</code> and can't be called from <code>A</code> -- Fix: change <code>A</code> to be a <code>struct</code></li> <li>This looks like a bug in VS10, even after all these fixes I get an error that you're trying to use an undefined class <code>B</code> in the <code>decltype</code>.</li> </ol> <p>As a workaround can you refactor <code>func</code> out into a base class? (now we need two template parameters, one for casting to and one for <code>decltype</code> thus creating a new idiom CRTPEX)</p> <pre><code>struct Base { void func() { } }; template<typename T, typename U> struct A { auto func() -> decltype(static_cast<T*>(nullptr)->func()) { return static_cast<U*>(this)->func(); } }; struct B : public A<Base, B>, public Base { }; </code></pre> <hr> <p>I see that g++ also chokes on this <code>decltype</code> can anyone confirm that this is a defect? If so I will open a bug for Microsoft. It is my understanding that the following code is valid but neither g++ nor VC10 compile it.</p> <pre><code>template<typename T> struct A { auto func() -> decltype(static_cast<T*>(nullptr)->func()) { return static_cast<T*>(this)->func(); } }; struct B : public A<B> { void func() {} }; </code></pre>

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