[cfe-users] Anyway to prevent this code from compiling?

[Brian Cole via cfe-users]

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:

OELock lock(mutex);

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:

#include <mutex>

using namespace std;

struct OEMutex
{
  void Acquire() {}
  void Release() {}
};

static OEMutex _mutex;

class OELock
{
  OEMutex &_mutex;
  OELock();
  OELock(const OELock&);
  OELock& operator=(const OELock&);

public:
  OELock(OEMutex &mutex) : _mutex(mutex) { _mutex.Acquire(); }
  ~OELock() { _mutex.Release(); }
};

int main()
{
  OELock lock(mutex);
}

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?).

Thanks,
Brian

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