[vwnc] VW object Identity
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I have a question about object identity.
Is there any way to the application to see object unique internal ID ? Here is the problem I came across recently: I do have Hierarchy of Classes such a ... ColorPresenter ColorPresenterLight ColorPresenterDark Two leaf classes are identical in terms of the class structure, however they do differ in some aspects of how they handle user inputs and present themselves on the UI. They also are used as Keys for some Dictionaries. In the past I did use the construct like follow someCondition ifTrue:[ aColorPresenerLight changeClassTo:ColorPresenerDark]. to quickly change the behavior and presentation. Now it seems that after I switch the class, The Identity of the object is changing as well . Does anybody have any information on what is happening with the objects Identity when changeClassTo: being used. _______________________________________________ vwnc mailing list [hidden email] http://lists.cs.uiuc.edu/mailman/listinfo/vwnc |
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changeClassTo: (and changeClassToThatOf:) should not change the identity.
You should be able to use "identityHash" to identity an object, at least in 32-bit VW. I don't know that this is guaranteed across releases or anything like that, but its what is used in IdentityXxx's collections. I use it during debugging (I added it to the inspector display for all classes) so I can easily see if I am looking at the same object from place to place. Mark Pirogovsky wrote: > I have a question about object identity. > > Is there any way to the application to see object unique internal ID ? > > Here is the problem I came across recently: > > I do have Hierarchy of Classes such a > ... > ColorPresenter > ColorPresenterLight > ColorPresenterDark > > Two leaf classes are identical in terms of the class structure, however > they do differ in some aspects of how they handle user inputs and > present themselves on the UI. > > They also are used as Keys for some Dictionaries. > > In the past I did use the construct like follow > > someCondition ifTrue:[ aColorPresenerLight > changeClassTo:ColorPresenerDark]. > > to quickly change the behavior and presentation. Now it seems that > after I switch the class, The Identity of the object is changing as well . > > Does anybody have any information on what is happening with the objects > Identity when changeClassTo: being used. > > > > _______________________________________________ > vwnc mailing list > [hidden email] > http://lists.cs.uiuc.edu/mailman/listinfo/vwnc > -- Dennis Smith +1 416.798.7948 Cherniak Software Development Corporation Fax: +1 416.798.0948 509-2001 Sheppard Avenue East [hidden email] Toronto, ON M2J 4Z8 sip:[hidden email] Canada http://www.CherniakSoftware.com Entrance off Yorkland Blvd south of Sheppard Ave east of the DVP _______________________________________________ vwnc mailing list [hidden email] http://lists.cs.uiuc.edu/mailman/listinfo/vwnc |
Re: [vwnc] VW object Identity
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In reply to this post by Mark Pirogovsky-3
Mark,
as Dennis points out the identityHash shouldn't change. You should confirm this. e.g. | myObject oldObject oldHash | myObject := oldObject := ColorPresenterLight new.
oldHash := myObject identityHash. myObject changeClassTo: ColorPresenterDark.
self assert: oldObject == newObject. self assert: myObject identityHash = oldHash
If the identityHash isn't changing, are you perhaps causing the hash to change by virtue of different definitions in the two classes and the object being in some non-identity Set or Dictionary?
On Wed, Feb 25, 2009 at 9:17 AM, Mark Pirogovsky <[hidden email]> wrote: I have a question about object identity. _______________________________________________ vwnc mailing list [hidden email] http://lists.cs.uiuc.edu/mailman/listinfo/vwnc |
Re: [vwnc] VW object Identity and identityHash
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In reply to this post by Dennis smith-4
I just run simple experiment with the identityHash
in my image Metaclass allInstances asSet size -- 6998 (Metaclass allInstances asSet collect:[:ea |ea identityHash])size --5919 There are plenty of classes in the Image which are different classes, but their identityHash is the same. So it appears that identityHash is not very reliable identity for an object. All of the IdentityXX collections do use #== along with the #identityHash to uniquely identify objects. Here is the method comment "Answer a SmallInteger that is equal to the identityHash of any object that is == to the receiver. When two objects are not ==, their identityHash values may or may not be the same. The identityHash value does not change across the life of the object." Dennis Smith wrote: > changeClassTo: (and changeClassToThatOf:) should not change the identity. > > You should be able to use "identityHash" to identity an object, at least > in 32-bit > VW. I don't know that this is guaranteed across releases or anything > like that, > but its what is used in IdentityXxx's collections. I use it during > debugging > (I added it to the inspector display for all classes) so I can easily > see if I am looking > at the same object from place to place. > > > Mark Pirogovsky wrote: >> I have a question about object identity. >> >> Is there any way to the application to see object unique internal ID ? >> >> Here is the problem I came across recently: >> >> I do have Hierarchy of Classes such a >> ... >> ColorPresenter >> ColorPresenterLight >> ColorPresenterDark >> >> Two leaf classes are identical in terms of the class structure, >> however they do differ in some aspects of how they handle user inputs >> and present themselves on the UI. >> >> They also are used as Keys for some Dictionaries. >> >> In the past I did use the construct like follow >> >> someCondition ifTrue:[ aColorPresenerLight >> changeClassTo:ColorPresenerDark]. >> >> to quickly change the behavior and presentation. Now it seems that >> after I switch the class, The Identity of the object is changing as >> well . >> >> Does anybody have any information on what is happening with the >> objects Identity when changeClassTo: being used. >> >> >> >> _______________________________________________ >> vwnc mailing list >> [hidden email] >> http://lists.cs.uiuc.edu/mailman/listinfo/vwnc >> > _______________________________________________ vwnc mailing list [hidden email] http://lists.cs.uiuc.edu/mailman/listinfo/vwnc |
Re: [vwnc] VW object Identity and identityHash
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On the other hand, the odds that two objects picked at random will have
the same identityHash is 1/16383 in a 32 bit image. What Dennis is doing is (I think) using identityHash in an inspector or equivalent to quickly determine if the two objects are being inspected are the same or not. In this case, the identityHash method would be reasonably accurate --- although one still has to rule out false positives. Andres. -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Mark Pirogovsky Sent: Wednesday, February 25, 2009 11:49 AM To: Dennis Smith Cc: VW NC Subject: Re: [vwnc] VW object Identity and identityHash I just run simple experiment with the identityHash in my image Metaclass allInstances asSet size -- 6998 (Metaclass allInstances asSet collect:[:ea |ea identityHash])size --5919 There are plenty of classes in the Image which are different classes, but their identityHash is the same. So it appears that identityHash is not very reliable identity for an object. All of the IdentityXX collections do use #== along with the #identityHash to uniquely identify objects. Here is the method comment "Answer a SmallInteger that is equal to the identityHash of any object that is == to the receiver. When two objects are not ==, their identityHash values may or may not be the same. The identityHash value does not change across the life of the object." Dennis Smith wrote: > changeClassTo: (and changeClassToThatOf:) should not change the identity. > > You should be able to use "identityHash" to identity an object, at > least in 32-bit VW. I don't know that this is guaranteed across > releases or anything like that, but its what is used in IdentityXxx's > collections. I use it during debugging (I added it to the inspector > display for all classes) so I can easily see if I am looking at the > same object from place to place. > > > Mark Pirogovsky wrote: >> I have a question about object identity. >> >> Is there any way to the application to see object unique internal ID >> >> Here is the problem I came across recently: >> >> I do have Hierarchy of Classes such a ... >> ColorPresenter >> ColorPresenterLight >> ColorPresenterDark >> >> Two leaf classes are identical in terms of the class structure, >> however they do differ in some aspects of how they handle user inputs >> and present themselves on the UI. >> >> They also are used as Keys for some Dictionaries. >> >> In the past I did use the construct like follow >> >> someCondition ifTrue:[ aColorPresenerLight >> changeClassTo:ColorPresenerDark]. >> >> to quickly change the behavior and presentation. Now it seems that >> after I switch the class, The Identity of the object is changing as >> well . >> >> Does anybody have any information on what is happening with the >> objects Identity when changeClassTo: being used. >> >> >> >> _______________________________________________ >> vwnc mailing list >> [hidden email] >> http://lists.cs.uiuc.edu/mailman/listinfo/vwnc >> > _______________________________________________ vwnc mailing list [hidden email] http://lists.cs.uiuc.edu/mailman/listinfo/vwnc _______________________________________________ vwnc mailing list [hidden email] http://lists.cs.uiuc.edu/mailman/listinfo/vwnc |
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