59 lines
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59 lines
5 KiB
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<title>CLiki: Issue INCOMPLETE-CLASS</title>
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<span class="hidden">CLiki - Issue INCOMPLETE-CLASS</span>
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<div id="content"><div id="content-area"><div id="article-title">Issue INCOMPLETE-CLASS</div><div id="article"><a href="Issue.html" class="category">Issue</a>: INCOMPLETE-CLASS<p>References: <a href="https://www.cliki.net/site/HyperSpec/Body/mac_defclass.html" class="hyperspec">DEFCLASS</a>, <a href="http://www.cliki.net/site/HyperSpec/Body/sec_4-3-1.html">4.3.1</a><p><dl><p><dt>Problem Description:</dt><p><dd>
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<a href="https://www.cliki.net/site/HyperSpec/Body/mac_defclass.html" class="hyperspec">DEFCLASS</a> states that for standard classes, "It is not required that the superclasses of a class be defined before the defclass form for that class is evaluated." Let's call such a class with a not-yet-defined superclass an "incomplete class". One can now argue whether an incomplete class is a class or not, i.e. if <a href="https://www.cliki.net/site/HyperSpec/Body/acc_find-class.html" class="hyperspec">FIND-CLASS</a> is required to return it, given its name.<p><ul>
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<li>Since <a href="https://www.cliki.net/site/HyperSpec/Body/mac_defclass.html" class="hyperspec">DEFCLASS</a> says "defclass defines a new named class", an incomplete class should be considered as a class.</li>
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<li>CLHS 4.3.1 says that a class determines the structure of a set of objects. This is not true for incomplete classes, as they cannot be instantiated.</li>
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<li>CLHS 4.3.1 says that each class has a class precedence list. Incomplete classes don't, since the complete list of superclasses is unknown.</li>
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<li>CLHS 4.3.1 says that the class t is a superclass of every class except itself. So there should be a chain of direct-superclass relations from an incomplete class to t. But for incomplete classes for which all direct superclasses don't exist yet there is no such chain.</li>
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</dd>
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</dl><p>You'll want to look into the <a href="MOP.html" class="internal">MOP</a>'s <a href="https://clos-mop.hexstreamsoft.com/classes/#forward-referenced-class">FORWARD-REFERENCED-CLASS</a>. Notably, <a href="https://clos-mop.hexstreamsoft.com/concepts/#inheritance-structure-of-metaobject-classes">Section 5.3 Inheritance structure of metaobject classes</a> and <a href="https://clos-mop.hexstreamsoft.com/concepts/#class-finalization-protocol">Section 5.5.2 Class finalization protocol</a> of <a href="AMOP.html" class="internal">AMOP</a> talk about it a bit.</div></div>
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