tutorial: "doesNotUnderstand" instance variable

I'm trying to go through the pipsqueak tutorial, but it throws a
doesNotUnderstand error when I try to initialize the exitSides instance
variable the first time.  The browser shows the exitSides variable (with
nil value), so the VM knows its there.

This is my class declaration:
Object subclass: #BlankCell
    instanceVariableNames: 'activeSegments exitSides'
    classVariableNames: ''
    poolDictionaries: ''
    category: 'Laser-Game-Model'

This is my init function:
initializeExitSides
    self exitSides: Dictionary new.
    self exitSides at: #north put: #south.
    self exitSides at: #east put: #west.
    self exitSides at: #south put: #north.
    self exitSides at: #west put: #east.

And a screen shot of my error stack trace is here:
  http://www.isi.edu/~amarshal/transfers/squeak_error.png
(How do I copy it as text anyway?)


Anm
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Andrew n marshall wrote: Use := when assigning variables.
Karl
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Karl a écrit : The error message says that #existSides: doesn't exist. So either you
create it (the accessor) or you directly affect the instance variable.

BlankCell>>existSide: aDictionary
        existSide := aDictionary

or you replace in you initialize method "self exitSides: Dictionary" new by:
existSide := Dictionary new
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On Nov 14, 2007, at 5:35 , Andrew n marshall wrote:

> And a screen shot of my error stack trace is here:
>  http://www.isi.edu/~amarshal/transfers/squeak_error.png
> (How do I copy it as text anyway?)

It is automatically saved as SqueakDebug.log.

- Bert -


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Cédrick Béler wrote:
> The error message says that #existSides: doesn't exist. So either you
> create it (the accessor) or you directly affect the instance variable.
>
> BlankCell>>existSide: aDictionary
>        existSide := aDictionary
>
> or you replace in you initialize method "self exitSides: Dictionary"
> new by:
> existSide := Dictionary new

Where are you getting "existSides"?  Everything I see in the stack
screen shot and in my email says "exitSides"?



I'm going to assume that was a mistake, and you're suggesting the same
thing Karl mentioned.

If I do this, it "doesNotUnderstand" the following line.  But I see the
var is set, so I remove self from all the following lines.  The accessor
complains similarly, and I remove self from it also.

It works, but I'm confused and concerned now.  Why does the tutorial (
http://squeak.preeminent.org/tut2007/html/021.html ) recommend the other
form, and why does that form work for activeSegments (my other instance
variable, which is also a Dictionary) but not exitSides:

initializeActiveSegments
    self activeSegments: Dictionary new.
    self activeSegments at: #north put: false.
    self activeSegments at: #east put: false.
    self activeSegments at: #south put: false.
    self activeSegments at: #west put: false.

In my mind, I now have two instance variables of Dictionarys that I have
to initialize and reference in different ways.

I just realized activeSegments has an accessor / mutator pair.  So, is
this an omission of the tutorial, forgetting to mention the those
methods?  Am I correct in concluding methods calls are always prefixed
by the class instance variable name (in this case "self) while instance
variables of self are referenced directly?
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I just noticed "As before, create accessors" on the tutorial page.

Still, that I can reference instance variables directly is
enlightening.  Does a subclass have the same access privilege, or must I
use accessors when reference superclass instance variables?


Anm
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