Thank you all for your replies. I would say, that “Class Variable” name is a bit misleading, but now I know what is going on behind it. :)
Cheers! Uko On 19 Mar 2014, at 23:53, Ben Coman <b...@openinworld.com> wrote: > Yuriy Tymchuk wrote: >> Can anybody tell me what is the difference between the class variable on the >> "instance side” definition and instance variable on the “class side” >> definition? >> >> Thanks in advance. >> Uko >> >> > instance-variable: A variable that holds the private state of an object. In > Smalltalk these can only be accessed by instance-methods. > > class-variable: An attribute of a class that is shared by that class, its > subclasses, and all instances of those classes. Can be accessed by > both instance-methods and class-methods. > > class-instance-variable: An attribute of a class that is not shared > outside that specific class. Only the definition is inherited by subclasses, > not the value . Each subclass has its own private value. Accessible only by > class-methods. > > > You will understand it best by experimenting. Here is one I made for > myself... > > ivCounter - instance variable counter > CVCounter - class variable counter > CIVCounter - class instance variable counter > > "----------" > Object subclass: #TestCounter > instanceVariableNames: 'ivCounter iName' > classVariableNames: 'CVCounter' > poolDictionaries: '' > category: 'MyExamples' > > TestCounter class "accessed by clicking the <Class> button" > instanceVariableNames: 'CIVCounter' > > TestCounter subclass: #TestSubCounter > instanceVariableNames: '' > classVariableNames: '' > poolDictionaries: '' > category: 'MyExamples' > "----------" > TestCounter name: myInstanceName > iName := myInstanceName. > TestCounter >> next > ivCounter ifNil: [ ivCounter := 0 ]. > CVCounter ifNil: [ CVCounter := 0 ]. > ivCounter := ivCounter + 1. > CVCounter := CVCounter + 1. > TestCounter >> printOn: aStream > super printOn: aStream. > aStream nextPutAll: ' ['. aStream > print: iName. > aStream nextPutAll: '] ( '. aStream > nextPutAll: ' ivCounter='; > print: ivCounter. > aStream > nextPutAll: ', CIVCounter=n/a'. > aStream > nextPutAll: ', CVCounter='; > print: CVCounter. > aStream nextPutAll: ' )'. "----------" TestCounter class >> next2 > CIVCounter ifNil: [ CIVCounter := 0 ]. > CVCounter ifNil: [ CVCounter := 0 ]. > > CIVCounter := CIVCounter + 1. > CVCounter := CVCounter + 1. > TestCounter class >> printOn: aStream > super printOn: aStream. > aStream nextPutAll: ' ( '. aStream > nextPutAll: 'ivCounter=n/a'. > aStream > nextPutAll: ', CIVCounter='; > print: CIVCounter. > aStream > nextPutAll: ', CVCounter='; > print: CVCounter. > aStream nextPutAll: ' )'. TestCounter class >> reset > CVCounter := nil. > CIVCounter := nil. > > "---------" > Then from Workspace evaluate these... > > tc1 := TestCounter new. > tc2 := TestCounter new. > > tsc1 := TestSubCounter new. > tsc2 := TestSubCounter new. > > TestCounter reset. > TestSubCounter reset. > > tc1 next. tc2 next. > tc1 next. > tc2 next. > > tsc1 next. > tsc2 next. > tsc1 next. > tsc2 next. > > TestCounter next2. > TestCounter next2. > TestCounter next2. > > > TestSubCounter next2. > TestSubCounter next2. > TestSubCounter next2. > > cheers -ben > > > > >
