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Since switching over to clang C++11 on OS X, we had this weird C++ oddity surface while writing some new code. The problem is that ‘mutex’ is no longer a variable, it is a class type that can be interpreted as a function argument. That is, the following line
of code can be interpreted as a function declaration now:</div>
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OELock lock(mutex);</div>
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Instead of a scoped lock acquisition as has been convention for some time now. The full code to recreate the subtle bug is as follows: </div>
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<div><font face="Calibri,sans-serif">#include <mutex></font></div>
<div><font face="Calibri,sans-serif"><br>
</font></div>
<div><font face="Calibri,sans-serif">using namespace std;</font></div>
<div><font face="Calibri,sans-serif"><br>
</font></div>
<div><font face="Calibri,sans-serif">struct OEMutex</font></div>
<div><font face="Calibri,sans-serif">{</font></div>
<div><font face="Calibri,sans-serif"> void Acquire() {}</font></div>
<div><font face="Calibri,sans-serif"> void Release() {}</font></div>
<div><font face="Calibri,sans-serif">};</font></div>
<div><font face="Calibri,sans-serif"><br>
</font></div>
<div><font face="Calibri,sans-serif">static OEMutex _mutex;</font></div>
<div><font face="Calibri,sans-serif"><br>
</font></div>
<div><font face="Calibri,sans-serif">class OELock</font></div>
<div><font face="Calibri,sans-serif">{</font></div>
<div><font face="Calibri,sans-serif"> OEMutex &_mutex;</font></div>
<div><font face="Calibri,sans-serif"> OELock();</font></div>
<div><font face="Calibri,sans-serif"> OELock(const OELock&);</font></div>
<div><font face="Calibri,sans-serif"> OELock& operator=(const OELock&);</font></div>
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<div><font face="Calibri,sans-serif">public:</font></div>
<div><font face="Calibri,sans-serif"> OELock(OEMutex &mutex) : _mutex(mutex) { _mutex.Acquire(); }</font></div>
<div><font face="Calibri,sans-serif"> ~OELock() { _mutex.Release(); }</font></div>
<div><font face="Calibri,sans-serif">};</font></div>
<div><font face="Calibri,sans-serif"><br>
</font></div>
<div><font face="Calibri,sans-serif">int main()</font></div>
<div><font face="Calibri,sans-serif">{</font></div>
<div><font face="Calibri,sans-serif"> OELock lock(mutex);</font></div>
<div><font face="Calibri,sans-serif">}</font></div>
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<div>Ideally, we would like the compilation to fail and tell the user the ‘mutex’ variable can not be found. Any clever C++ trick to do that? We’ve tried declaring the move constructors of OELock to be private, but it still compiles (maybe that’s SFINAE?). </div>
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<div>Thanks,</div>
<div>Brian</div>
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