92 lines
8.5 KiB
HTML
92 lines
8.5 KiB
HTML
<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
|
|
<HTML>
|
|
<HEAD>
|
|
<TITLE>CLHS: Accessor GETF</TITLE>
|
|
<LINK HREF="../Data/clhs.css" REL="stylesheet" TYPE="text/css" />
|
|
<META HTTP-EQUIV="Author" CONTENT="Kent M. Pitman">
|
|
<META HTTP-EQUIV="Organization" CONTENT="LispWorks Ltd.">
|
|
<LINK REL=TOP HREF="../Front/index.htm">
|
|
<LINK REL=COPYRIGHT HREF="../Front/Help.htm#Legal">
|
|
<LINK REL=DISCLAIMER HREF="../Front/Help.htm#Disclaimer">
|
|
<LINK REL=PREV HREF="f_get_pr.htm">
|
|
<LINK REL=UP HREF="c_conses.htm">
|
|
<LINK REL=NEXT HREF="m_remf.htm">
|
|
</HEAD>
|
|
<BODY>
|
|
<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="f_get_pr.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_conses.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="m_remf.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
|
|
|
|
<HR>
|
|
|
|
<A NAME="getf"><I>Accessor</I> <B>GETF</B></A> <P>
|
|
<P><B>Syntax:</B><P>
|
|
<P>
|
|
|
|
<B>getf</B> <I>plist indicator <TT>&optional</TT> default</I> => <I>value</I><P>
|
|
|
|
<TT>(setf (</TT><B>getf</B> <I>place indicator <TT>&optional</TT> default</I><TT>) </TT><I>new-value</I><TT>)</TT><P>
|
|
<P>
|
|
<P><B>Arguments and Values:</B><P>
|
|
<P>
|
|
<I>plist</I>---a <A REL=DEFINITION HREF="26_glo_p.htm#property_list"><I>property list</I></A>. <P>
|
|
<I>place</I>---a <A REL=DEFINITION HREF="26_glo_p.htm#place"><I>place</I></A>, the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of which is a <A REL=DEFINITION HREF="26_glo_p.htm#property_list"><I>property list</I></A>. <P>
|
|
<I>indicator</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
|
|
<I>default</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. The default is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
|
|
<I>value</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
|
|
<I>new-value</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
|
|
<P><B>Description:</B><P>
|
|
<P>
|
|
<A REL=DEFINITION HREF="#getf"><B>getf</B></A> finds a <A REL=DEFINITION HREF="26_glo_p.htm#property"><I>property</I></A> on the <I>plist</I> whose <A REL=DEFINITION HREF="26_glo_p.htm#property_indicator"><I>property indicator</I></A> is <A REL=DEFINITION HREF="26_glo_i.htm#identical"><I>identical</I></A> to <I>indicator</I>, and returns its corresponding <A REL=DEFINITION HREF="26_glo_p.htm#property_value"><I>property value</I></A>. If there are multiple <A REL=DEFINITION HREF="26_glo_p.htm#property"><I>properties</I></A>[1] with that <A REL=DEFINITION HREF="26_glo_p.htm#property_indicator"><I>property indicator</I></A>, <A REL=DEFINITION HREF="#getf"><B>getf</B></A> uses the first such <A REL=DEFINITION HREF="26_glo_p.htm#property"><I>property</I></A>. If there is no <A REL=DEFINITION HREF="26_glo_p.htm#property"><I>property</I></A> with that <A REL=DEFINITION HREF="26_glo_p.htm#property_indicator"><I>property indicator</I></A>, <I>default</I> is returned. <P>
|
|
<A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> of <A REL=DEFINITION HREF="#getf"><B>getf</B></A> may be used to associate a new <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A> with an existing indicator in the <A REL=DEFINITION HREF="26_glo_p.htm#property_list"><I>property list</I></A> held by <I>place</I>, or to create a new assocation if none exists. If there are multiple <A REL=DEFINITION HREF="26_glo_p.htm#property"><I>properties</I></A>[1] with that <A REL=DEFINITION HREF="26_glo_p.htm#property_indicator"><I>property indicator</I></A>, <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> of <A REL=DEFINITION HREF="#getf"><B>getf</B></A> associates the <I>new-value</I> with the first such <A REL=DEFINITION HREF="26_glo_p.htm#property"><I>property</I></A>. When a <A REL=DEFINITION HREF="#getf"><B>getf</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> is used as a <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> <I>place</I>, any <I>default</I> which is supplied is evaluated according to normal left-to-right evaluation rules, but its <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> is ignored. <P>
|
|
<A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> of <A REL=DEFINITION HREF="#getf"><B>getf</B></A> is permitted to either <A REL=DEFINITION HREF="26_glo_w.htm#write"><I>write</I></A> the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of <I>place</I> itself, or modify of any part, <A REL=DEFINITION HREF="26_glo_c.htm#car"><I>car</I></A> or <A REL=DEFINITION HREF="26_glo_c.htm#cdr"><I>cdr</I></A>, of the <A REL=DEFINITION HREF="26_glo_l.htm#list_structure"><I>list structure</I></A> held by <I>place</I>. <P><B>Examples:</B><P>
|
|
<P>
|
|
|
|
<PRE>
|
|
(setq x '()) => NIL
|
|
(getf x 'prop1) => NIL
|
|
(getf x 'prop1 7) => 7
|
|
(getf x 'prop1) => NIL
|
|
(setf (getf x 'prop1) 'val1) => VAL1
|
|
(eq (getf x 'prop1) 'val1) => <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
|
|
(getf x 'prop1) => VAL1
|
|
(getf x 'prop1 7) => VAL1
|
|
x => (PROP1 VAL1)
|
|
|
|
;; Examples of implementation variation permitted.
|
|
(setq foo (list 'a 'b 'c 'd 'e 'f)) => (A B C D E F)
|
|
(setq bar (cddr foo)) => (C D E F)
|
|
(remf foo 'c) => <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
|
|
foo => (A B E F)
|
|
bar
|
|
=> (C D E F)
|
|
OR=> (C)
|
|
OR=> (NIL)
|
|
OR=> (C NIL)
|
|
OR=> (C D)
|
|
</PRE>
|
|
</TT> <P>
|
|
<P><B>Side Effects:</B> None.
|
|
<P>
|
|
<P><B>Affected By:</B> None.
|
|
<P>
|
|
<P><B>Exceptional Situations:</B> None.
|
|
<P>
|
|
<P><B>See Also:</B><P>
|
|
<P>
|
|
<A REL=DEFINITION HREF="f_get.htm#get"><B>get</B></A>, <A REL=DEFINITION HREF="f_get_pr.htm#get-properties"><B>get-properties</B></A>, <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A>, <A REL=CHILD HREF="05_abb.htm">Section 5.1.2.2 (Function Call Forms as Places)</A> <P>
|
|
<P><B>Notes:</B><P>
|
|
<P>
|
|
There is no way (using <A REL=DEFINITION HREF="#getf"><B>getf</B></A>) to distinguish an absent property from one whose value is <I>default</I>; but see <A REL=DEFINITION HREF="f_get_pr.htm#get-properties"><B>get-properties</B></A>. <P>
|
|
Note that while supplying a <I>default</I> argument to <A REL=DEFINITION HREF="#getf"><B>getf</B></A> in a <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> situation is sometimes not very interesting, it is still important because some macros, such as <A REL=DEFINITION HREF="m_push.htm#push"><B>push</B></A> and <A REL=DEFINITION HREF="m_incf_.htm#incf"><B>incf</B></A>, require a <I>place</I> argument which data is both <A REL=DEFINITION HREF="26_glo_r.htm#read"><I>read</I></A> from and <I>written</I> to. In such a context, if a <I>default</I> argument is to be supplied for the <A REL=DEFINITION HREF="26_glo_r.htm#read"><I>read</I></A> situation, it must be syntactically valid for the <A REL=DEFINITION HREF="26_glo_w.htm#write"><I>write</I></A> situation as well. For example, <P>
|
|
<PRE>
|
|
(let ((plist '()))
|
|
(incf (getf plist 'count 0))
|
|
plist) => (COUNT 1)
|
|
</PRE>
|
|
</TT> <P>
|
|
<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss293.htm">REMF-DESTRUCTION-UNSPECIFIED:X3J13-MAR-89</A><LI> <A REL=CHILD HREF="../Issues/iss306.htm">SETF-GET-DEFAULT:EVALUATED-BUT-IGNORED</A><LI> <A REL=CHILD HREF="../Issues/iss269.htm">PLIST-DUPLICATES:ALLOW</A><P></UL><HR>
|
|
|
|
<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
|
|
|
|
<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
|
|
</BODY>
|
|
</HTML>
|