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50 lines
5.2 KiB
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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: Section 7.1.7</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="07_af.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="07_a.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="07_b.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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7.1.7 Definitions of Make-Instance and Initialize-Instance</H2> <P>
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The generic function <A REL=DEFINITION HREF="f_mk_ins.htm#make-instance"><B>make-instance</B></A> behaves as if it were defined as follows, except that certain optimizations are permitted: <P>
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<PRE>
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(defmethod make-instance ((class standard-class) &rest initargs)
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...
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(let ((instance (apply #'allocate-instance class initargs)))
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(apply #'initialize-instance instance initargs)
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instance))
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(defmethod make-instance ((class-name symbol) &rest initargs)
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(apply #'make-instance (find-class class-name) initargs))
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</PRE>
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</TT> <P>
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The elided code in the definition of <A REL=DEFINITION HREF="f_mk_ins.htm#make-instance"><B>make-instance</B></A> augments the <TT>initargs</TT> with any <I>defaulted initialization arguments</I> and checks the resulting initialization arguments to determine whether an initialization argument was supplied that neither filled a <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> nor supplied an argument to an applicable <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A>. <P>
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The generic function <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"><B>initialize-instance</B></A> behaves as if it were defined as follows, except that certain optimizations are permitted: <P>
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<PRE>
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(defmethod initialize-instance ((instance standard-object) &rest initargs)
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(apply #'shared-initialize instance t initargs)))
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</PRE>
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</TT> <P>
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These procedures can be customized. <P>
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Customizing at the Programmer Interface level includes using the <TT>:initform</TT>, <TT>:initarg</TT>, and <TT>:default-initargs</TT> options to <A REL=DEFINITION HREF="m_defcla.htm#defclass"><B>defclass</B></A>, as well as defining <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> for <A REL=DEFINITION HREF="f_mk_ins.htm#make-instance"><B>make-instance</B></A>, <A REL=DEFINITION HREF="f_alloca.htm#allocate-instance"><B>allocate-instance</B></A>, and <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"><B>initialize-instance</B></A>. It is also possible to define <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> for <A REL=DEFINITION HREF="f_shared.htm#shared-initialize"><B>shared-initialize</B></A>, which would be invoked by the generic functions <A REL=DEFINITION HREF="f_reinit.htm#reinitialize-instance"><B>reinitialize-instance</B></A>, <A REL=DEFINITION HREF="f_upda_1.htm#update-instance-for-redefined-class"><B>update-instance-for-redefined-class</B></A>, <A REL=DEFINITION HREF="f_update.htm#update-instance-for-different-class"><B>update-instance-for-different-class</B></A>, and <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"><B>initialize-instance</B></A>. The meta-object level supports additional customization. <P>
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Implementations are permitted to make certain optimizations to <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"><B>initialize-instance</B></A> and <A REL=DEFINITION HREF="f_shared.htm#shared-initialize"><B>shared-initialize</B></A>. The description of <A REL=DEFINITION HREF="f_shared.htm#shared-initialize"><B>shared-initialize</B></A> in Chapter 7 mentions the possible optimizations. <P>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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