On Dec 4, 2004, at 8:56 PM, Doug Way wrote:

>
> On Dec 4, 2004, at 11:21 PM, Aaron Gray wrote:
>>  What about messages to instance variables ?
>
> Not sure what you mean here.  If you can get to the instance variable,  
> you can send a message to it.  (It is true that you can't reference an  
> object's instance variable directly unless you are "inside" that  
> object.  Smalltalk instance variables have the equivalent of  
> "protected" access in C++/Java-speak.)
>
> - Doug

Well I'll actually point out that normally if you don't have an  
accessor method for an instance variable the you shouldn't be able to  
access that instance variable outside the class
But to preserve the sanity of folks who want to something clever we  
provide a way  you can cheat.

Object>>instVarAt: index
	"Primitive. Answer a fixed variable in an object. The numbering of the
	variables corresponds to the named instance variables. Fail if the  
index
	is not an Integer or is not the index of a fixed variable. Essential.  
See
	Object documentation whatIsAPrimitive."

	<primitive: 73>
	"Access beyond fixed variables."
	^self basicAt: index - self class instSize		

To poke at instance variables that you don't have access to.
The reason for doing this usually implies something very clever, say  
serializling an object to be sent over the internet, or
printing the contents of an object on the error log.  However, doing  
this as part of any non-clever drab business program is as
you might guess a frowned upon activity...


Aaron I'll point out an instance variable is just a placeholder for any  
smalltalk object, which could be a number, a Class, an Array, a drab  
business object. There is
no type restrictions or naming conventions that dictate terms/rules.  
Beyond the acceptable practices that Class variables start with upper  
case, and rules for how
instance variables are named, methods named etc. Again these are all  
styles the community uses, see "Smalltalk with Style" for the rules.  
Smalltalk is very clever and
flexible, none of the restrictions you are use to in other languages.


Try this link for some free smalltalk books
http://www.iam.unibe.ch/~ducasse/FreeBooks.html


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John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
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