>
>Basically, I'm trying to create relationships between objects using
>Association. But I became alarmed today when I did the following:
>
>assoc := Association new.
>
>aKey := 'keystring'.
>aValue := 'valuestring'.
>
>assoc key: aKey value: aValue.
>
>aValue := 'new value'.
>
>assoc value  ==>  'valuestring'
>
>This made me think that the association was storing a *copy* of aValue in
>its own instance.
>
>Exactly what is going on in this situation?
>

Well 'valuestring' is a instance of a String object floating about 
referenced by  aKey and then via an instance var in assoc, so both 
aKey and the instance var in assoc point to that string instance. 
Unless of course assoc->key:value: makes a copy (doubtful).

When you change the reference aValue to point to the other string 
object 'new value' that doesn't change the reference to 'valuestring' 
because the instance var in the instance of assoc is still point to 
it.

Now if you where to directly alter the string by manipulating aValue 
that would have implications. (aKey at: 2 put: $x) then look at assoc 
value

Of course when you remove all references to the 'valuestring' then it 
will become garbage and be collected at some future point.

String constants need a bit of care, to ensure you don't alter them 
and everyone else who refers to them, and of course string constants 
that are the same within a method might have different behavior ie == 
depending on the flavor of Smalltalk you use. mmm for example 'abc' 
== 'abc' might not be true since there could be two string objects 
here depending on what the parser does. This only bites the unwary 
and I think most current Smalltalk have worked around this issue. MMm 
I think it was early versions of visualage that inflicted that gem on 
us, no?
-- 
--
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John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
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