C++ foward structures

The syntax for forward declaring structs in a namespace wasn't immediatly intuitive to me.

// Bar.h 
namespace MikesHax 
{ 
   class Bar { 
      public: Bar( int inVal ); 
      private: int mVal; }; 
} 

// Foo.h 
// Note we don't include Bar.h 
namespace MikesHax 
{ 
   class Bar; 
} 

class Foo { public: Foo( MikesHax::Bar const &inBar ); };

When Full Declarations Are Not Required