108 lines
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108 lines
5.9 KiB
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Converted with LaTeX2HTML 0.6.5 (Tue Nov 15 1994) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE>28.1.9.7. Definitions of Make-Instance and Initialize-Instance</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Definitions of Make-Instance and Initialize-Instance">
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<meta name="keywords" value="clm">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html5393 HREF="node300.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5391 HREF="node292.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5387 HREF="node298.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5395 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5396 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5394 HREF="node300.html"> Redefining Classes</A>
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<B>Up:</B> <A NAME=tex2html5392 HREF="node292.html"> Object Creation and </A>
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<B> Previous:</B> <A NAME=tex2html5388 HREF="node298.html"> Initialize-Instance</A>
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<HR> <P>
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<H3><A NAME=SECTION003219700000000000000>28.1.9.7. Definitions of Make-Instance and Initialize-Instance</A></H3>
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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The generic function <tt>make-instance</tt> behaves as if it were defined as
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follows, except that certain optimizations are permitted:
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<P>
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<P>
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<P><pre>
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(defmethod make-instance ((class standard-class) &rest initargs)
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(setq initargs (default-initargs class 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)) <BR><BR>(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><P>
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<P>
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<P>
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The elided code in the definition of <tt>make-instance</tt> checks the
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supplied initialization arguments to determine whether an initialization
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argument was supplied that neither filled a slot nor supplied an argument
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to an applicable method. This check could be implemented using the generic
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functions <tt>class-prototype</tt>, <tt>compute-applicable-methods</tt>,
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<tt>function-keywords</tt>, and <tt>class-slot-initargs</tt>. See the third
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part of the Common Lisp Object System specification for a
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description of this initialization argument check.
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[The third part
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has not yet been approved by X3J13 for inclusion in the forthcoming
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Common Lisp standard and is not included in this book.-GLS]
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<P>
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The generic function <tt>initialize-instance</tt> behaves as if it were
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defined as follows, except that certain optimizations are permitted:
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<P>
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<P><pre>
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(defmethod initialize-instance
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((instance standard-object) &rest initargs)
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(apply #'shared-initialize instance t initargs)))
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</pre><P>
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<P>
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These procedures can be customized at either the Programmer Interface level,
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the meta-object level, or both.
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<P>
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Customizing at the Programmer Interface level includes using the
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<tt>:initform</tt>, <tt>:initarg</tt>, and <tt>:default-initargs</tt> options to
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<tt>defclass</tt>, as well as defining methods for <tt>make-instance</tt>
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and <tt>initialize-instance</tt>. It is also possible to define
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methods for <tt>shared-initialize</tt>, which would be invoked by the
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generic functions <tt>reinitialize-instance</tt>,
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<tt>update-instance-for-redefined-class</tt>,
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<tt>update-instance-for-different-class</tt>, and
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<tt>initialize-instance</tt>. The meta-object level supports additional
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customization by allowing methods to be defined on
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<tt>make-instance</tt>, <tt>default-initargs</tt>, and
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<tt>allocate-instance</tt>. Parts 2 and 3 of the Common Lisp Object System specification document each of these generic
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functions and the system-supplied primary methods.
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[The third part
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has not yet been approved by X3J13 for inclusion in the forthcoming
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Common Lisp standard and is not included in this book.-GLS]
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<P>
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Implementations are permitted to make certain optimizations to
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<tt>initialize-instance</tt> and <tt>shared-initialize</tt>. The
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description of <tt>shared-initialize</tt> in
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section <A HREF="node311.html#FunctionsintheProgrammerInterfaceSECTION">28.2</A>
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mentions the
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possible optimizations.
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<P>
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Because of optimization, the check for valid initialization arguments
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might not be implemented using the generic functions
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<tt>class-prototype</tt>, <tt>compute-applicable-methods</tt>,
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<tt>function-keywords</tt>, and <tt>class-slot-initargs</tt>. In addition,
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methods for the generic function <tt>default-initargs</tt> and the
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system-supplied primary methods for <tt>allocate-instance</tt>,
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<tt>initialize-instance</tt>,
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and <tt>shared-initialize</tt> might not be called on
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every call to <tt>make-instance</tt> or might not receive exactly the
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arguments that would be expected.
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<BR> <HR><A NAME=tex2html5393 HREF="node300.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5391 HREF="node292.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5387 HREF="node298.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5395 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5396 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5394 HREF="node300.html"> Redefining Classes</A>
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<B>Up:</B> <A NAME=tex2html5392 HREF="node292.html"> Object Creation and </A>
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<B> Previous:</B> <A NAME=tex2html5388 HREF="node298.html"> Initialize-Instance</A>
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<HR> <P>
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<HR>
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<P><ADDRESS>
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AI.Repository@cs.cmu.edu
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</ADDRESS>
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