NAME¶

TF_2Port, TF_Direct - transfer function subclasses

SYNOPSIS¶

#include <Unidraw/transfns.h>

DESCRIPTION¶

The TransferFunct abstract base class defines the transfer functionprotocol. The library predefines two subclasses. TF_2Port is asubclass that acts as an abstract base class for transfer functionshaving two sets of state variables, ``input'' and ``output'', withoutput variables always dependent on input variables. TF_Direct is asubclass of TF_2Port that defines a one-to-one assignment relationshipbetween an input and an output state variable.

TF_2PORTPUBLICOPERATIONS¶

void Evaluate(Path* = nil)

Evaluate first carries out information transfer between dependentstate variables by calling the Transfer operation (described below).Then it iterates through its output state variables; those that havechanged (according to the ChangedOutput operation, described below)get Transmit called on the connector they're bound to. Subclassesneedn't redefine this operation if they implement Transfer andChangedOutput 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. Theseoperations return zero by default.

TF_2PORTPROTECTEDOPERATIONS¶

TF_2Port()

The constructor is protected to prevent instantiation.

virtual void Transfer()

Enforce the subclass-specific dependencies between the TF_2Port'sstate variables. This operation does nothing by default.

virtual boolean ChangedOutput(int index = 0)

Return whether the output state variable with the given index haschanged its value since the last call to Transfer. Subclassesredefine this operation according to the semantics of their Transferoperation.

TF_DIRECTPUBLICOPERATIONS¶

TF_Direct(StateVar* input = nil, StateVar* output = nil)

Instantiate a new object, optionally specifying the input statevariable 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_Directdefines 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. Theseoperations return zero by default.

virtual int Inputs()

virtual int Outputs()

These operations return 1.

TF_DIRECTPROTECTEDOPERATIONS¶

virtual void Transfer()

Assign the input state variable to the output state variable, settinga 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 aside-effect of this operation.

SEEALSO¶

TransferFunct(3U)