org.abora.white.stepper
Class EmptyStepper

java.lang.Object
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  +--org.abora.white.xpp.basic.Heaper
        |
        +--org.abora.white.collection.steppers.Stepper
              |
              +--org.abora.white.stepper.EmptyStepper

public class EmptyStepper

extends Stepper

This is a Stepper when you just want to step across a single item.

Field Summary

Fields inherited from class org.abora.white.collection.steppers.Stepper

TheEmptyStepper

Constructor Summary

EmptyStepper()

Method Summary

Stepper	copy() Return a new stepper which steps independently of me, but whose current value is the same as mine, and which must produce a future history of values which satisfies the same obligation that my contract obligates me to produce now.
void	destroy() No
void	destruct() This object is a canonical single instance, so its destructor should only be called after main has exited.
Heaper	fetch() If I am exhausted (i.e., if (!! this->hasValue())), then return NULL.
boolean	hasValue() Iff I have a current value (i.e.
void	step() Essential.

Methods inherited from class org.abora.white.collection.steppers.Stepper

actualHashForEqual, atEnd, emptyStepper, get, info, isEqual, itemStepper, stepMany, stepMany, theOne

Methods inherited from class org.abora.white.xpp.basic.Heaper

equals, hashForEqual, printContentsOn, printOn, sendSelfTo, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

EmptyStepper

public EmptyStepper()

Method Detail

destruct

public void destruct()

This object is a canonical single instance, so its destructor should only be called after main has exited.

Overrides:

destruct in class Heaper

copy

public Stepper copy()

Description copied from class: Stepper

Return a new stepper which steps independently of me, but whose current value is the same as mine, and which must produce a future history of values which satisfies the same obligation that my contract obligates me to produce now. Typically, this will mean that he must produce the same future history that I'm going to produce. However, let's say that I am enumerating the elements of a partial order in some full order which is consistent with the partial order. If a copy of me is made after I'm part way through, then me and my copy may produce any future history compatable both with the partial order and the elements I've already produced by the time of the copy. Of course, a subclass or a Stepper creating message (like IntegerRegion::stepper()) may specify the more stringent requirement (that a copy must produce the same sequence). To prevent aliasing, Steppers should typically be passed by copy. See class comment.

Specified by:

copy in class Stepper

destroy

public void destroy()

No

Overrides:

destroy in class Heaper

fetch

public Heaper fetch()

Description copied from class: Stepper

If I am exhausted (i.e., if (!! this->hasValue())), then return NULL. Else return current element. I return wimpily since most items returned are held by collections. If I create a new object, I should cache it.

Specified by:

fetch in class Stepper

hasValue

public boolean hasValue()

Description copied from class: Stepper

Iff I have a current value (i.e. this message returns true), then I am not exhasted. 'fetch' and 'get' will both return this value, and I can be 'step'ped to my next state. As I am stepped, eventually I may become exhausted (the reverse of all the above), which is a permanent condition. Note that not all steppers have to be exhaustable. A Stepper which enumerates all primes is perfectly reasonable. Assuming otherwise will create infinite loops. See class comment.

Specified by:

hasValue in class Stepper

step

public void step()

Description copied from class: Stepper

Essential. If I am currently exhausted (see Stepper::hasValue()), then it is an error to step me. The result of doing so isn't currently specified (we probably should specify it to BLAST, but I know that the implementation doesn't currently live up to that spec). If I am not exhausted, then this advances me to my next state. If my current value (see Stepper::get()) was my final value, then I am now exhausted, otherwise my new current value is the next value.

Specified by:

step in class Stepper