lementations of several member functions.
</P>

<P>
    The template <A href="../classes/device.html"><CODE>device</CODE></A> and its specializations <A HREF="../classes/device.html#synopsis"><CODE>source</CODE></A> and <A HREF="../classes/device.html#synopsis"><CODE>sink</CODE></A> help users define new Device types; the template <A href="../classes/filter.html"><CODE>filter</CODE></A> and its specializations <A HREF="../classes/filter.html#synopsis"><CODE>input_filter</CODE></A> and <A HREF="../classes/fi