// file: library.h
#ifndef LIBRARY_H
#define LIBRARY_H

namespace Foo
{
  enum SensorStatus
  {
     PreInit,
     Initialized
  };
};

#endif

// file: sensor.h
#ifndef SENSOR_H
#define SENSOR_H

#include "library.h"

namespace Foo
{
  class Sensor
  {
     public:
     Sensor();
     SensorStatus Status = SensorStatus.PreInit; // ERROR
   };
};

error: 'SensorStatus' does not name a type
SensorStatus Status = SensorStatus.PreInit;