TF_2Port, TF_Direct - transfer function subclasses

SYNOPSIS

       #include <Unidraw/transfns.h>

DESCRIPTION

       The TransferFunct abstract base class defines the transfer
       function protocol.  The library predefines two subclasses.
       TF_2Port is a subclass that acts as an abstract base class
       for transfer functions having two sets of state variables,
       ``input''  and  ``output'',  with  output variables always
       dependent on input variables.  TF_Direct is a subclass  of
       TF_2Port that defines a one-to-one assignment relationship
       between an input and an output state variable.

TF_2PORT PUBLIC OPERATIONS

       void Evaluate(Path* = nil)
              Evaluate first  carries  out  information  transfer
              between  dependent  state  variables by calling the
              Transfer  operation  (described  below).   Then  it
              iterates  through its output state variables; those
              that have changed (according to  the  ChangedOutput
              operation,  described below) get Transmit called on
              the connector they're bound to.  Subclasses needn't
              redefine  this operation if they implement Transfer
              and ChangedOutput appropriately.

       virtual StateVar* GetInput(int index)
       virtual StateVar* GetOutput(int index)
       virtual void SetInput(StateVar*, int index)
       virtual void SetOutput(StateVar*, int index)
              Retrieve and assign the TF_2Port's input and output
              state variables, identified serially.  These opera-
              tions do nothing by default; subclasses must  allo-
              cate the storage they require.

       virtual int Inputs()
       virtual int Outputs()
              Return  the  number of input and output state vari-
              ables.  These operations return zero by default.

TF_2PORT PROTECTED OPERATIONS

       TF_2Port()
              The constructor is protected to prevent  instantia-
              tion.

       virtual void Transfer()
              Enforce  the subclass-specific dependencies between
              the TF_2Port's  state  variables.   This  operation
              does nothing by default.

       virtual boolean ChangedOutput(int index = 0)
              call  to Transfer.  Subclasses redefine this opera-
              tion according to the semantics of  their  Transfer
              operation.

TF_DIRECT PUBLIC OPERATIONS

       TF_Direct(StateVar* input = nil, StateVar* output = nil)
              Instantiate a new object, optionally specifying the
              input state variable and its dependent output state
              variable.

       virtual StateVar* GetInput(int index = 0)
       virtual StateVar* GetOutput(int index = 0)
       virtual void SetInput(StateVar*, int index = 0)
       virtual void SetOutput(StateVar*, int index = 0)
              Retrieve  and assign the TF_Direct's input and out-
              put state variables.  Specifying an  index  greater
              than  zero  does nothing, since TF_Direct defines a
              dependency between one input and one  output  state
              variable.

       virtual int Inputs()
       virtual int Outputs()
              Return  the  number of input and output state vari-
              ables.  These operations return zero by default.

       virtual int Inputs()
       virtual int Outputs()
              These operations return 1.

TF_DIRECT PROTECTED OPERATIONS

       virtual void Transfer()
              Assign the input state variable to the output state
              variable, setting a flag indicating that the output
              value has changed.

       virtual boolean ChangedOutput(int index = 0)
              Return the status of the flag set by Transfer.  The
              flag is reset as a side-effect of this operation.

SEE ALSO

       TransferFunct(3U)