"

 COPYRIGHT (c) 1992 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.

"

Dictionary subclass:#IdentityDictionary

       instanceVariableNames:''

       classVariableNames:''

       poolDictionaries:''

       category:'Collections-Unordered'

!

IdentityDictionary comment:'

COPYRIGHT (c) 1992 by Claus Gittinger

              All Rights Reserved

same as a Dictionary but key must be identical - not just equal.

Since compare is on identity keys, hashing is also done via

identityHash instead of hash.

%W% %E%

written jul 92 by claus

'!

!IdentityDictionary methodsFor:'private'!

findKeyOrNil:key

    "Look for the key in the receiver.  If it is found, return

     the index of the association containing the key, otherwise

     return the index of the first unused slot. Grow the receiver,

     if key was not found, and no unused slots where present"

    |index  "{ Class:SmallInteger }"

     length "{ Class:SmallInteger }"

     startIndex

     probe |

    length := keyArray basicSize.

    startIndex := key identityHash \\ length + 1.

    index := startIndex.

    [true] whileTrue:[

        probe := keyArray basicAt:index.

        (probe isNil or: [probe == key]) ifTrue:[^ index].

        index == length ifTrue:[

            index := 1

        ] ifFalse:[

            index := index + 1

        ].

        index == startIndex ifTrue:[^ self grow findKeyOrNil:key].

    ]

!

findKey:key ifAbsent:aBlock

    "Look for the key in the receiver.  If it is found, return

     the index of the association containing the key, otherwise

     return the value of evaluating aBlock."

    |index  "{ Class:SmallInteger }"

     length "{ Class:SmallInteger }"

     startIndex

     probe|

    length := keyArray basicSize.

    length < 10 ifTrue:[

        "assuming, that for small dictionaries the overhead of hashing

         is large ... maybe that proves wrong (if overhead of comparing

         is high)"

        index := keyArray identityIndexOf:key.

        index == 0 ifTrue:[

            ^ aBlock value

        ].

        ^ index

    ].

    startIndex := key identityHash \\ length + 1.

    index := startIndex.

    [true] whileTrue:[

        probe := keyArray basicAt:index.

        probe == key ifTrue:[^ index].

        index == length ifTrue:[

            index := 1

        ] ifFalse:[

            index := index + 1

        ].

        (probe isNil or:[index == startIndex]) ifTrue:[^ aBlock value]

    ]

! !