"

 COPYRIGHT (c) 1989 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

"{ Package: 'stx:libbasic' }"

SequenceableCollection subclass:#LinkedList

	instanceVariableNames:'firstLink lastLink numberOfNodes'

	classVariableNames:''

	poolDictionaries:''

	category:'Collections-Linked'

!

!LinkedList class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1989 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

!

documentation

"

    this class implements an anchor to a list of Links.

    See (the abstract) Link, ValueLink and (possibly other) classes,

    which can be used as elements of a linkedList.

    LinkedList does not care for storage; all it does is handling

    chained link elements, which must respond to #nextLink/#nextLink:.

    (i.e. any object which can do this, can be used as elements of a linked

    An abstract superclass for linkElements is Link; a concrete class is

    ValueLink, which holds a reference to some object.

    [warning:]

    Although LinkedList is a subclass of SequenceableCollection (and therefore

    supports indexed access via at:), you should be careful in using it or

    The reason is that #at: walks the linkedlist to find the indexed element

    SequenceableCollection become square in runtime.

    In general, if you need access via a numeric index, you better use Array,

    OrderedCollection or similar.

    For the above reasons, the system does not make heavily use of LinkedLists;

    the only good application is where elements must be repeatedly be removed

    at the front and added at the end.

    (the schedulers process handling code does this to manage process lists.)

    [memory requirements:]

    [author:]

    [see also:]

"

!

"

    |l|

    l := LinkedList new.

    l addLast:(ValueLink new value:'one').

    l addLast:(ValueLink new value:'two').

    l addLast:(ValueLink new value:'three').

    l addLast:(ValueLink new value:'four').

    l inspect

    |l|

    l := LinkedList new.

    l addLast:(ValueLink new value:'one').

    l addLast:(ValueLink new value:'two').

    l addLast:(ValueLink new value:'three').

    l addLast:(ValueLink new value:'four').

    (l at:3) value inspect.        'slow operation for large lists'.

    |l link|

    l := LinkedList new.

    l addLast:(ValueLink new value:'one').

    l addLast:(ValueLink new value:'two').

    l addLast:(ValueLink new value:'three').

    l addLast:(ValueLink new value:'four').

    link := l removeFirst.

    l addLast:link.

"

! !

!LinkedList class methodsFor:'instance creation'!

new

    "create and return a new LinkedList"

    ^ self basicNew initialize

! !

!LinkedList methodsFor:'accessing'!

at:index

    "return the n'th element - use of this method should be avoided,

     since it is slow to walk through the list - think about using

     another collection if you need indexed access.

     Notice, that many methods in SeqColl are based on at:-access,

     so other inherited methods may be very slow (showing square runtime)."

    ^ self at:index ifAbsent:[ self subscriptBoundsError:index]

!

at:index ifAbsent:exceptionBlock

    "return the n'th element - use of this method should be avoided,

     since it is slow to walk through the list - think about using

     another collection if you need indexed access.

     Notice, that many methods in SeqColl are based on at:-access,

     so other inherited methods may be very slow (showing square runtime)."

    |theLink

     runIndex "{Class: SmallInteger}"|

    theLink := firstLink.

    runIndex := 1.

    [runIndex == index] whileFalse:[

    ].

    ^ theLink

!

first

    "return the first node in the list"

    firstLink isNil ifTrue:[^ self emptyCollectionError].

    ^ firstLink

!

last

    "return last node in the list"

    lastLink isNil ifTrue:[self emptyCollectionError].

    ^ lastLink

! !

!LinkedList methodsFor:'adding & removing'!

add:aLink

    "adds aLink to the end of the sequence. Returns aLink"

    aLink nextLink:nil.

    lastLink isNil ifTrue:[

	firstLink := aLink

    ] ifFalse: [

	lastLink nextLink:aLink

    ].

    lastLink := aLink.

    numberOfNodes := numberOfNodes + 1.

    ^ aLink

!

add:linkToAdd after:aLink

    "adds linkToAdd after another link, aLink. If aLink is nil,

     linkToAdd is inserted at the beginning. Returns linkToAdd."

    |this|

    aLink isNil ifTrue:[^ self addFirst:linkToAdd ].

    this := firstLink.

    [this notNil and:[this ~~ aLink]] whileTrue:[

	this := this nextLink

    ].

    this isNil ifTrue:[^ self add:linkToAdd ].

    linkToAdd nextLink:(this nextLink).

    this nextLink:linkToAdd.

    ^ linkToAdd

!

addFirst:aLink

    "adds aLink to the beginning of the sequence. Returns aLink"

    firstLink isNil ifTrue:[

    ].

    numberOfNodes := numberOfNodes + 1.

    ^ aLink

!

remove:aLink ifAbsent:exceptionBlock

     if absent, evaluate the exceptionBlock.

     Actually this is really a #removeIdentical (but for compatibility ...)"

    |prevNode nextNode thisNode|

    thisNode := firstLink.

    [thisNode notNil] whileTrue:[

    ].

    ^ exceptionBlock value

    "Modified: 1.2.1997 / 12:01:59 / cg"

!

removeAll

    "remove all elements from the sequence. Returns the receiver."

    firstLink := lastLink := nil.

    numberOfNodes := 0

    "Created: 21.3.1996 / 15:24:38 / cg"

    "Modified: 12.4.1996 / 13:34:53 / cg"

!

removeFirst

    "remove and return the first node from the sequence"

    |link|

    firstLink isNil ifTrue:[

    ].

    link := firstLink.

    ].

    link nextLink:nil.

    numberOfNodes := numberOfNodes - 1.

    ^ link

! !

!LinkedList methodsFor:'enumerating'!

do:aBlock

    "evaluate the argument, aBlock with 1 arg for every element in the list"

    |thisNode|

    thisNode := firstLink.

    [thisNode notNil] whileTrue:[

	aBlock value:thisNode.

	thisNode := thisNode nextLink

    ]

! !

!LinkedList methodsFor:'initialization'!

initialize

    numberOfNodes := 0

! !

!LinkedList methodsFor:'queries'!

size

    "return the size of the LinkedList i.e. the number of nodes"

    ^ numberOfNodes

! !

!LinkedList methodsFor:'testing'!

    "search the collection for aLink, starting the search at index start;

     if found, return the index otherwise return 0. Here, index is defined

     as the link-nodes position in the list.

     (i.e. equality test - not identity test)."

    |theNode idx "{ Class: SmallInteger }"|

    theNode := firstLink.

    idx := 1.

    [idx < start] whileTrue:[

	theNode isNil ifTrue:[^ 0].     "reached the end"

	theNode := theNode nextLink.

	idx := idx + 1.

    ].

    [theNode notNil] whileTrue:[

	(aLink == theNode) ifTrue:[^ idx].

	theNode := theNode nextLink.

	idx := idx + 1.

    ].                                  "reached the end"

    ^ 0

    "

     |l|

     l := LinkedList new.

    "

    "

     |l v|

     l := LinkedList new.

     l add:(ValueLink new value:'one').

     l add:(ValueLink new value:'two').

     l add:(v := ValueLink new value:'hello').

    "

!

    "search the collection for aLink, starting the search at index start;

     if found, return the index otherwise return 0. Here, index is defined

     as the link-nodes position in the list.

     The comparison is done using = (i.e. equality test - not identity test)."

    |theNode idx "{ Class: SmallInteger }"|

    theNode := firstLink.

    idx := 1.

    [idx < start] whileTrue:[

	theNode isNil ifTrue:[^ 0].     "reached the end"

	theNode := theNode nextLink.

	idx := idx + 1.

    ].

    [theNode notNil] whileTrue:[

	(aLink = theNode) ifTrue:[^ idx].

	theNode := theNode nextLink.

	idx := idx + 1.

    ].                                  "reached the end"

    ^ 0

    "

     |l|

     l := LinkedList new.

    "

    "

     |l v|

     l := LinkedList new.

     l add:(ValueLink new value:'one').

     l add:(ValueLink new value:'two').

     l add:(v := ValueLink new value:'hello').

    "

!

isEmpty

    "return true, if the collection is empty"

    ^ firstLink isNil

!

notEmpty

    "return true, if the collection is not empty"

    ^ firstLink notNil

! !

!LinkedList class methodsFor:'documentation'!

version

! !