issue with answer http://stackoverflow.com/a/9954553/192737

#include <memory>

class foo
{
    class impl;
    std::unique_ptr<impl> impl_;

public:
    ~foo(); // Implement (with an empty body) where impl is complete
//   foo();   // <-- adding this to the example will cause compile to pass again
};

int main() {
   foo bar;
   return 0;
}