[Boost-users] query regarding mutex

Hello All, This is how mutex class looks like #include class mutex: boost::noncopyable { public: mutex(); ~mutex(); void lock(); bool try_lock(); void unlock(); typedef platform-specific-type native_handle_type; native_handle_type native_handle(); typedef unique_lock<mutex> scoped_lock; typedef unspecified-type scoped_try_lock; }; Please help me figure out what purpose does 'unspecified-type' serve below. typedef unspecified-type scoped_try_lock; as I understand typedef type_a name_a ; enables name_a to be used instead of type_a what does unspecified-type stand for ? and how does one use it ? regards Abhishek