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100 lines
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<H2>Issue SETF-FIND-CLASS Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss304.htm">SETF-FIND-CLASS</A><P>
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<P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/f_find_c.htm#find-class"><B>FIND-CLASS</B></A> in 88-002R<P>
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<P>
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<B>Category:</B> CLARIFICATION<P>
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<P>
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<B>Edit history:</B> 29-Apr-90, Version 1 by Moon<P>
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30-Apr-90, Version 2 by Moon (update current practice)<P>
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2-May-90, Version 3 by Moon (remove incorrect reference<P>
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to Loosemore issue #7 of 27 Feb 90)<P>
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4-May-90, Version 4 by Moon (update discussion and current<P>
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practice)<P>
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<P>
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<B>Problem description:<P>
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</B><P>
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Is (<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> (<A REL=DEFINITION HREF="../Body/f_find_c.htm#find-class"><B>FIND-CLASS</B></A> 'FOO) <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>) permitted as a way to break the link from<P>
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a name to a class? I can't find anything in the CLOS spec for or against<P>
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this.<P>
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<P>
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This is Symbolics issue #27.<P>
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<P>
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<B>Proposal (SETF-FIND-CLASS:ALLOW-NIL):<P>
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</B><P>
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Define (<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> (<A REL=DEFINITION HREF="../Body/f_find_c.htm#find-class"><B>FIND-CLASS</B></A> 'FOO) <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>) to cause FOO no longer to name a <A REL=DEFINITION HREF="../Body/t_class.htm#class"><B>class</B></A>.<P>
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If FOO already does not name a <A REL=DEFINITION HREF="../Body/t_class.htm#class"><B>class</B></A>, the operation has no effect.<P>
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<P>
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This does not affect the <A REL=DEFINITION HREF="../Body/t_class.htm#class"><B>class</B></A> formerly named by FOO, if any, except that<P>
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if FOO was that <A REL=DEFINITION HREF="../Body/t_class.htm#class"><B>class</B></A>'s proper name, the <A REL=DEFINITION HREF="../Body/t_class.htm#class"><B>class</B></A> no longer has a proper name.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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This is simpler than putting in a new function to break the association<P>
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between a name and a <A REL=DEFINITION HREF="../Body/t_class.htm#class"><B>class</B></A>. When CMAKUNBOUND was removed from an early<P>
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draft of 88-002R, it was probably intended to add this <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> of <A REL=DEFINITION HREF="../Body/f_find_c.htm#find-class"><B>FIND-CLASS</B></A><P>
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feature to replace it, but the document was accidentally not updated.<P>
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<P>
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<B>Current practice:<P>
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</B><P>
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Symbolics Genera 8.0, TI Explorer release 6.0, and Lucid 4.0.0 Beta-1<P>
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implement the proposal. Other CLOS implementations were not surveyed.<P>
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<P>
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<B>Cost to Implementors:<P>
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</B><P>
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Easy.<P>
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<P>
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<B>Cost to Users:<P>
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</B><P>
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None.<P>
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<P>
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<B>Cost of non-adoption:<P>
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</B><P>
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There will be no portable way to break the association between a name and<P>
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a <A REL=DEFINITION HREF="../Body/t_class.htm#class"><B>class</B></A>.<P>
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<P>
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<B>Performance impact:<P>
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</B><P>
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None.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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Adds a useful feature that was probably intended to be there all along.<P>
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<P>
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<B>Esthetics:<P>
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</B><P>
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More complete language.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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Gregor Kiczales says he supports <A HREF="iss304.htm">SETF-FIND-CLASS:ALLOW-NIL</A>.<P>
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</PRE>
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