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Hi Mark,<br>
<br>
Interesting exercise!<br>
<br>
Doing `self become: ` is dangerous and tricky. The very method doing
that will continue execution, but now the receiver is of a different
class! This would crash the system if that methods tries to access
instance variables that are not there. The control in #become: that
bothers you is trying to protect you from that risk.<br>
<br>
I suggest slightly different code, to avoid doing `self become:`:
move the sends to #become. to the class side. So:<br>
<br>
class side<br>
on: anObject<br>
| proxy |<br>
proxy := self new on: anObject.<br>
anObject become: proxy.<br>
^proxy<br>
<br>
instance side<br>
on: anObject<br>
history := OrderedCollection new.<br>
object := anObject shallowCopy.<br>
" anObject become: self"<br>
<br>
and class side<br>
restoreAndProvideHistory: aProxy<br>
| result |<br>
result := aProxy history.<br>
aProxy become: aProxy object.<br>
^result<br>
<br>
Also add the two needed getters #history and #object. Now the
workspace example does:<br>
<br>
history := HistoryProxy restoreAndProvideHistory: date.<br>
<br>
This doesn't need any modification to #become:, is more robust and
future proof, and better style.<br>
<br>
Cheers,<br>
<br>
On 1/26/2025 4:56 PM, Mark Volkmann via Cuis-dev wrote:
<blockquote
cite="mid:CAFfRWnV3+3A0Jz1uzMDiZm2ACHEDjZMdhxem4z+HfzPohGKeKg@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>I recently read the book "Discovering Smalltalk". I know
it's quite dated and it's based on Smalltalk/V instead of
Smalltalk-80, but I still learned a lot from it.</div>
<div><br>
</div>
<div>I implement the Gatekeeper example described on pages
428-430 in Cuis. It demonstrates using the <font
face="monospace">becomes:</font> method to track all
messages sent to a given object. I got it working, but I had
to make a small modification to the <font face="monospace">ProtoObject</font>
instance method <font face="monospace">becomes:</font>. I'm
wondering if my change would break other uses of this method.</div>
<div><br>
</div>
<div>I replaced the line</div>
<div><br>
</div>
<div><font face="monospace">selfMethod =
otherObjectMethod ifFalse: [<br>
</font></div>
<div><br>
</div>
<div>with</div>
<div><br>
</div>
<div><font face="monospace">selfMethod ~= nil and:<br>
[otherObjectMethod ~= nil] and:<br>
[selfMethod ~= otherObjectMethod] :: ifTrue: [<br>
</font></div>
<div><br>
</div>
<div>Here's my working Gatekeeper code where I renamed that
class to HistoryProxy.</div>
<div><br>
</div>
<div><font face="monospace">Object subclass: #HistoryProxy<br>
instanceVariableNames: 'history object'<br>
classVariableNames: ''<br>
poolDictionaries: ''<br>
category: 'Demo'<br>
</font></div>
<div><font face="monospace"><br>
</font></div>
<div><font face="monospace">"class method"</font></div>
<div><font face="monospace">on: anObject<br>
^ self new on: anObject<br>
</font></div>
<div><font face="monospace"><br>
</font></div>
<div><font face="monospace">"instance method"</font></div>
<div><font face="monospace">on: anObject<br>
history := OrderedCollection new.<br>
object := anObject shallowCopy.<br>
anObject become: self<br>
</font></div>
<div><font face="monospace"><br>
</font></div>
<div><font face="monospace">"instance method"</font></div>
<div><font face="monospace">doesNotUnderstand: aMessage<br>
"Record the message and reroute it to the object."<br>
</font>
<div><span style="font-family: monospace;"> history add:
aMessage.</span><br>
</div>
<font face="monospace"> ^ aMessage sendTo: object.<br>
</font></div>
<div><font face="monospace"><br>
</font></div>
<div><font face="monospace">"instance method"</font></div>
<div><font face="monospace">restoreAndProvideHistory<br>
</font><font face="monospace"> | result |<br>
</font><span style="font-family: monospace;"> "Extract
information before mutating because it won't be available
afterwards."</span><br style="font-family: monospace;">
<font face="monospace"> result := history.<br>
self become: object.<br>
^ result.</font><br>
</div>
<div><br>
</div>
<div>Here's an example of using this:</div>
<div><br>
</div>
<div><font face="monospace">date := Date today.<br>
HistoryProxy on: date.<br>
date monthName print.<br>
date dayOfWeekName print.<br>
date year print.<br>
history := date restoreAndProvideHistory.<br>
history print "an OrderedCollection(monthName dayOfWeekName
year)"</font><br>
</div>
<div><br>
</div>
<span class="gmail_signature_prefix">-- </span><br>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr">
<div>
<div dir="ltr">
<div>
<div dir="ltr">
<div dir="ltr">
<div><font face="arial, helvetica, sans-serif">R.
Mark Volkmann</font></div>
<div><span style="font-size: 12.8px;"><font
face="arial, helvetica, sans-serif">Object
Computing, Inc.</font></span></div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Juan Vuletich
cuis.st
github.com/jvuletich
researchgate.net/profile/Juan-Vuletich
independent.academia.edu/JuanVuletich
patents.justia.com/inventor/juan-manuel-vuletich
linkedin.com/in/juan-vuletich-75611b3
twitter.com/JuanVuletich</pre>
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