NAME

       TransferFunct - transfer function base class

SYNOPSIS

       #include <Unidraw/transfn.h>

DESCRIPTION

       A  transfer function defines relationships between state variables.  A component uses a transfer function
       to enforce dependencies between its state variables during dataflow. State variables whose values  change
       as  a result of data flowing into the component can thus affect the component's dependent state variables
       as defined by its transfer function.  A transfer function can define dependencies between any  number  of
       state variables, but a component can define only one transfer function.

PUBLIC OPERATIONS

       virtual void Evaluate(Path* = nil)
              Enforce  the transfer function's dependencies between its state variables, optionally depending on
              the information in a path.  This operation does nothing by default.

       virtual TransferFunct* Copy()
              Return a copy of the transfer function.  Subclasses redefine this operation to return an  instance
              of their type.

       virtual void Read(istream&)
       virtual void Write(ostream&)
              Read  and  write the transfer function's contents to a stream to support catalog operations.  Read
              and write typically call first the corresponding operations defined by  their  parent  class,  and
              then they read or write their class-specific state.

       virtual ClassId GetClassId()
       virtual boolean IsA(ClassId)
              GetClassId  returns  the unique class identifier for the TransferFunct subclass, while IsA returns
              whether the instance is of a class  or  subclass  corresponding  to  the  given  identifier.   IsA
              typically  checks  the  given  identifier against the instance's own (as defined by its GetClassId
              operation) and, failing that, calls its  parent  classes'  IsA  operation.   All  subclasses  must
              redefine  GetClassId  and  IsA  to ensure that their identifiers are unique and that instances are
              written and read properly.

PROTECTED OPERATIONS

       TransferFunct()
              The constructor is protected to prevent instantiation.

       virtual Connector* GetBinding(StateVar*)
              Return the connector to which a state variable is bound.

SEE ALSO

       Catalog(3U),   Component(3U),   Connector(3U),   Creator(3U),   Path(3U),    StateVar(3U)    classes(3U),
       istream(3C++), ostream(3C++)

Unidraw                                           6 August 1990                                TransferFunct(3U)