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<p>> <span style="font-size: 12pt;">x := Compiler evaluate: 'super identityHash' for: ProtoObject new.</span></p>
<div>> <span style="font-size: 12pt;">thisContext objectClass: x.</span></div>
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<p><span style="font-size: 12pt;">Also interesting:</span><br>
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<p>'super bar' returns a DNU where the receiver is a SmallInteger (sic!). In a second image, the call is skipped, again ...</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Von:</b> Squeak-dev <squeak-dev-bounces@lists.squeakfoundation.org> im Auftrag von Thiede, Christoph<br>
<b>Gesendet:</b> Samstag, 5. September 2020 13:10:29<br>
<b>An:</b> Squeak Dev<br>
<b>Betreff:</b> [squeak-dev] Two new questions about VM machinery :-)</font>
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<p>Hi all, hi Eliot,</p>
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<p>just for curiosity, I have two new questions <span style="font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols; font-size: 16px;">about the VM machinery</span> (which
are far away from praxis but close to my interests):</p>
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</span></p>
<p><span style="font-size: 12pt;"><b>1.</b></span><span style="font-size: 12pt;"><b> super on ProtoObject</b></span></p>
<p><span style="font-size: 12pt;">What would you expect the following to return?</span></p>
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<div>x := Compiler evaluate: 'super identityHash' for: ProtoObject new.</div>
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<div>thisContext objectClass: x.</div>
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I would have guessed that either the VM crashes or ProtoObject >> #<span>cannotInterpret: is called.</span>
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<div class="_rp_T4" id="Item.MessagePartBody">But actually, it answers you the ProtoObject instance, which I find very interesting because it means that if a message cannot be looked up, it is simply and silently skipped.
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<div><font size="3" color="black"><span style="font-size:12pt"><a href="http://www.hpi.de/" target="_blank" rel="noopener noreferrer" id="LPNoLP"><font size="2"><span id="LPlnk909538"><font color="#757B80"></font></span></font></a></span></font></div>
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<div class="_rp_T4" id="Item.MessagePartBody">If you debug the call instead (Context class >> #runSimulated:), <span>Context >> #send:to:with:lookupIn: raises a nil DNU error, which makes more sense but unfortunately is not consistent with the original VM behavior.</span></div>
<div class="_rp_T4" id="Item.MessagePartBody"><span>Maybe the Compiler should forbid any call to super from ProtoObject instances at all (more formally: if the receiver's class's superclass is nil)? Or should we adjust the simulation code?</span></div>
<div class="_rp_T4" id="Item.MessagePartBody"><span>(By the way: If you do the same in Squeak.js, you'll get an infinite recursion :D)</span></div>
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<div class="_rp_T4" id="Item.MessagePartBody"><span><b>2. Mirror primitives</b></span></div>
<div class="_rp_T4" id="Item.MessagePartBody"><span>What is the reason for primitives such as 75 (#identityHash) or 78/139 (#nextInstance/#nextObject) not being mirrored in Context?</span></div>
<div class="_rp_T4" id="Item.MessagePartBody"><span>Was this simply forgotten, or don't we have the claim to mirror any "essential" primitive without it actually being needed by the simulation machinery?</span></div>
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<div class="_rp_T4" id="Item.MessagePartBody"><span>As always, looking forward to your interesting explanations! :-)</span></div>
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<div class="_rp_T4" id="Item.MessagePartBody"><span>Best,</span></div>
<div class="_rp_T4" id="Item.MessagePartBody"><span>Christoph</span></div>
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