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#include <mutex>
 
class Foo
{
 private:
  std::mutex lock_;
 
 public:
  Foo() = default;
  ~Foo() = default;
 
  void bad();
  void good();
};
 
void Foo::bad()
{
  std::lock_guard<std::mutex>(lock_);
}
 
void Foo::good()
{
  std::lock_guard<std::mutex>(this->lock_);
}
 
int main()
{
  return 0;
}
 

prog.cpp: In member function 'void Foo::bad()':
prog.cpp:18:36: error: no matching function for call to 'std::lock_guard<std::mutex>::lock_guard()'
   std::lock_guard<std::mutex>(lock_);
                                    ^
In file included from prog.cpp:1:0:
/usr/include/c++/5/mutex:379:7: note: candidate: std::lock_guard<_Mutex>::lock_guard(std::lock_guard<_Mutex>::mutex_type&, std::adopt_lock_t) [with _Mutex = std::mutex; std::lock_guard<_Mutex>::mutex_type = std::mutex]
       lock_guard(mutex_type& __m, adopt_lock_t) : _M_device(__m)
       ^
/usr/include/c++/5/mutex:379:7: note:   candidate expects 2 arguments, 0 provided
/usr/include/c++/5/mutex:376:16: note: candidate: std::lock_guard<_Mutex>::lock_guard(std::lock_guard<_Mutex>::mutex_type&) [with _Mutex = std::mutex; std::lock_guard<_Mutex>::mutex_type = std::mutex]
       explicit lock_guard(mutex_type& __m) : _M_device(__m)
                ^
/usr/include/c++/5/mutex:376:16: note:   candidate expects 1 argument, 0 provided

Standard output is empty