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<TITLE>CLHS: Issue SETF-FUNCTIONS-AGAIN Writeup</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="../Issues/iss304_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="../Issues/iss305.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="../Issues/iss306_w.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>Issue SETF-FUNCTIONS-AGAIN Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss305.htm">SETF-FUNCTIONS-AGAIN</A><P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A>, <A REL=DEFINITION HREF="../Body/f_fbound.htm#fboundp"><B>FBOUNDP</B></A>, <A REL=DEFINITION HREF="../Body/f_fdefin.htm#fdefinition"><B>FDEFINITION</B></A>, <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A><P>
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Related issues: Issue <A HREF="iss174.htm">FUNCTION-NAME</A><P>
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Issue <A HREF="iss310.htm">SETF-OF-APPLY</A><P>
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<B>Category:</B> CLARIFICATION<P>
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<B>Edit history:</B> V1, 13 May 90, Sandra Loosemore<P>
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<P>
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<B>Problem description:<P>
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</B><P>
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The addition of <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions to the language has left some<P>
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lingering questions:<P>
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<P>
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- Whether (<A REL=DEFINITION HREF="../Body/f_fbound.htm#fboundp"><B>FBOUNDP</B></A> '(<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> <name>)) is supposed to be true of <name>s <P>
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that have <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> methods (as defined with <A REL=DEFINITION HREF="../Body/m_defset.htm#defsetf"><B>DEFSETF</B></A> or DEFINE-SETF-METHOD)<P>
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defined, or only <name>s where there are globally defined<P>
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functions named (<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> <name>). (Issue #17 from Loosemore's<P>
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list.)<P>
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<P>
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- Whether <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A> is required to generate <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions, or required<P>
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to generate <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> methods, or whether this is unspecified. (Issue<P>
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#19)<P>
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<P>
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- Whether <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> places defined in the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> are required to be<P>
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implemented by <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions, by <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> methods, or whether this<P>
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is unspecified. (Issue #20)<P>
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<P>
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- Whether it is permissible for a <name> to have both a <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A><P>
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<A REL=DEFINITION HREF="../Body/t_method.htm#method"><B>method</B></A> defined via <A REL=DEFINITION HREF="../Body/m_defset.htm#defsetf"><B>DEFSETF</B></A> or DEFINE-SETF-METHOD, and an associated<P>
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<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> function at the same time. <P>
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<P>
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<P>
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<B>Proposal (SETF-FUNCTIONS-AGAIN:MINIMAL-CHANGES):<P>
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</B><P>
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(1) Clarify that (<A REL=DEFINITION HREF="../Body/f_fbound.htm#fboundp"><B>FBOUNDP</B></A> '(<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> <name>)) must return true if and<P>
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only if there is a function named (<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> <name>) defined. It must<P>
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return <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A> if <name> has a <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> <A REL=DEFINITION HREF="../Body/t_method.htm#method"><B>method</B></A> defined but not a <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A><P>
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function.<P>
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<P>
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(2) Clarify that it is unspecified whether <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A> generates<P>
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<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> methods or <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions for non-:READ-ONLY slot accessors.<P>
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<P>
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(3) Clarify that, unless a <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> function is explicitly documented<P>
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in the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A>, it is unspecified whether <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> places defined in<P>
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the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> must be implemented as <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> methods or <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions.<P>
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In combination with item (1), this implies that it is unspecified<P>
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whether (<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> <name>) is <A REL=DEFINITION HREF="../Body/f_fbound.htm#fboundp"><B>FBOUNDP</B></A> for these <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A><P>
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places.<P>
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<P>
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(4) Clarify that it is possible, but generally not very useful, <P>
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to have both a <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> <A REL=DEFINITION HREF="../Body/t_method.htm#method"><B>method</B></A> and a <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> function defined for the same<P>
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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 proposal requires minimal changes for implementors.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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Most implementations use <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> methods (and not <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions)<P>
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to implement <A REL=DEFINITION HREF="../Body/m_defstr.htm#defstruct"><B>DEFSTRUCT</B></A> accessors and the <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> places.<P>
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In most implementations, the namespaces for <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> methods and<P>
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<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions are disjoint.<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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Probably none.<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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Probably 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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Imprecision in the language specification.<P>
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<P>
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<B>Performance impact:<P>
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</B><P>
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Probably not significant.<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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The language specification is made more precise.<P>
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<P>
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<B>Esthetics:<P>
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</B><P>
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It would probably be better to specify whether <A REL=DEFINITION HREF="../Body/07_ffb.htm#standard"><B>standard</B></A> <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A><P>
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places must be implemented as <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> functions or as <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A><P>
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methods, instead of leaving it explicitly vague. See also<P>
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issue <A HREF="iss310.htm">SETF-OF-APPLY</A> for one particular case (<A REL=DEFINITION HREF="../Body/f_aref.htm#aref"><B>AREF</B></A>) where it<P>
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seems like a good idea to specify that the <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> place must be<P>
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implemented as a <A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>SETF</B></A> function.<P>
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<P>
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<B>Discussion:<P>
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</B></PRE>
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