transfns(3U)						    InterViews Reference Manual 					      transfns(3U)

NAME

       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 sub-
       class 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  imple-
	      ment 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 operations do nothing by default;
	      subclasses must allocate the storage they require.

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

TF_2PORT PROTECTED OPERATIONS
       TF_2Port()
	      The constructor is protected to prevent instantiation.

       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)
	      Return whether the output state variable with the given index has changed its value since the last  call	to  Transfer.	Subclasses
	      redefine this operation 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 output 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 variables.  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)

Unidraw 							   6 August 1990						      transfns(3U)