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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Standard Generic Function UPDATE-INSTANCE-FOR-REDEFINED-CLASS</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="f_update.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_object.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_chg_cl.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="update-instance-for-redefined-class"><I>Standard Generic Function</I> <B>UPDATE-INSTANCE-FOR-REDEFINED-CLASS</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>update-instance-for-redefined-class</B> <I>instance added-slots discarded-slots property-list <TT>&rest</TT> initargs <TT>&key</TT> <TT>&allow-other-keys</TT></I><P> => <I><I>result</I><B>*</B></I><P>
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<P>
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<P><B>Method Signatures:</B><P>
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<P>
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<B>update-instance-for-redefined-class</B> <I>(<I>instance</I><B> <A REL=DEFINITION HREF="t_std_ob.htm#standard-object">standard-object</A></B>) added-slots discarded-slots property-list <TT>&rest</TT> initargs</I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>instance</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<I>added-slots</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. <P>
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<I>discarded-slots</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. <P>
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<I>property-list</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. <P>
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<I>initargs</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#initialization_argument_list"><I>initialization argument list</I></A>. <P>
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<I>result</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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The <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> is not intended to be called by programmers. Programmers may write <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> for it. The <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> is called by the mechanism activated by <A REL=DEFINITION HREF="f_mk_i_1.htm#make-instances-obsolete"><B>make-instances-obsolete</B></A>. <P>
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The system-supplied primary <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> on <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> checks the validity of <I>initargs</I> and signals an error if an <I>initarg</I> is supplied that is not declared as valid. This <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> then initializes <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A> with values according to the <I>initargs</I>, and initializes the newly <I>added-slots</I> with values according to their <TT>:initform</TT> forms. It does this by calling the generic function <A REL=DEFINITION HREF="f_shared.htm#shared-initialize"><B>shared-initialize</B></A> with the following arguments: the <I>instance</I>, a list of names of the newly <I>added-slots</I> to <I>instance</I>, and the <I>initargs</I> it received. Newly <I>added-slots</I> are those <A REL=DEFINITION HREF="26_glo_l.htm#local_slot"><I>local slots</I></A> for which no <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> of the same name exists in the old version of the <A REL=DEFINITION HREF="26_glo_c.htm#class"><I>class</I></A>. <P>
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When <A REL=DEFINITION HREF="f_mk_i_1.htm#make-instances-obsolete"><B>make-instances-obsolete</B></A> is invoked or when a <A REL=DEFINITION HREF="26_glo_c.htm#class"><I>class</I></A> has been redefined and an <A REL=DEFINITION HREF="26_glo_i.htm#instance"><I>instance</I></A> is being updated, a <I>property-list</I> is created that captures the slot names and values of all the <I>discarded-slots</I> with values in the original <I>instance</I>. The structure of the <I>instance</I> is transformed so that it conforms to the current class definition. The arguments to <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> are this transformed <I>instance</I>, a list of <I>added-slots</I> to the <I>instance</I>, a list <I>discarded-slots</I> from the <I>instance</I>, and the <I>property-list</I> containing the slot names and values for <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A> that were discarded and had values. Included in this list of discarded <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A> are <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A> that were local in the old <A REL=DEFINITION HREF="26_glo_c.htm#class"><I>class</I></A> and are shared in the new <A REL=DEFINITION HREF="26_glo_c.htm#class"><I>class</I></A>. <P>
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The value returned by <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> is ignored. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(defclass position () ())
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(defclass x-y-position (position)
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((x :initform 0 :accessor position-x)
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(y :initform 0 :accessor position-y)))
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;;; It turns out polar coordinates are used more than Cartesian
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;;; coordinates, so the representation is altered and some new
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;;; accessor methods are added.
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(defmethod update-instance-for-redefined-class :before
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((pos x-y-position) added deleted plist &key)
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;; Transform the x-y coordinates to polar coordinates
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;; and store into the new slots.
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(let ((x (getf plist 'x))
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(y (getf plist 'y)))
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(setf (position-rho pos) (sqrt (+ (* x x) (* y y)))
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(position-theta pos) (atan y x))))
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(defclass x-y-position (position)
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((rho :initform 0 :accessor position-rho)
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(theta :initform 0 :accessor position-theta)))
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;;; All instances of the old x-y-position class will be updated
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;;; automatically.
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;;; The new representation is given the look and feel of the old one.
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(defmethod position-x ((pos x-y-position))
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(with-slots (rho theta) pos (* rho (cos theta))))
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(defmethod (setf position-x) (new-x (pos x-y-position))
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(with-slots (rho theta) pos
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(let ((y (position-y pos)))
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(setq rho (sqrt (+ (* new-x new-x) (* y y)))
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theta (atan y new-x))
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new-x)))
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(defmethod position-y ((pos x-y-position))
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(with-slots (rho theta) pos (* rho (sin theta))))
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(defmethod (setf position-y) (new-y (pos x-y-position))
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(with-slots (rho theta) pos
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(let ((x (position-x pos)))
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(setq rho (sqrt (+ (* x x) (* new-y new-y)))
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theta (atan new-y x))
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new-y)))
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</PRE>
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</TT> <P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B><P>
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The system-supplied primary <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> on <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> signals an error if an <I>initarg</I> is supplied that is not declared as valid. <P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_mk_i_1.htm#make-instances-obsolete"><B>make-instances-obsolete</B></A>, <A REL=DEFINITION HREF="f_shared.htm#shared-initialize"><B>shared-initialize</B></A>, <A REL=CHILD HREF="04_cf.htm">Section 4.3.6 (Redefining Classes)</A>, <A REL=CHILD HREF="07_ad.htm">Section 7.1.4 (Rules for Initialization Arguments)</A>, <A REL=CHILD HREF="07_ab.htm">Section 7.1.2 (Declaring the Validity of Initialization Arguments)</A> <P>
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<P><B>Notes:</B><P>
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<P>
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<I>Initargs</I> are declared as valid by using the <TT>:initarg</TT> option to <A REL=DEFINITION HREF="m_defcla.htm#defclass"><B>defclass</B></A>, or by defining <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> for <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> or <A REL=DEFINITION HREF="f_shared.htm#shared-initialize"><B>shared-initialize</B></A>. The keyword name of each keyword parameter specifier in the <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list"><I>lambda list</I></A> of any <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> defined on <A REL=DEFINITION HREF="#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A> or <A REL=DEFINITION HREF="f_shared.htm#shared-initialize"><B>shared-initialize</B></A> is declared as a valid <I>initarg</I> name for all <A REL=DEFINITION HREF="26_glo_c.htm#class"><I>classes</I></A> for which that <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is applicable. <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issue</A>, <I>not part of the specification</I>, applies to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss197.htm">INITIALIZATION-FUNCTION-KEYWORD-CHECKING</A><P></UL><HR>
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