87 lines
4.9 KiB
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87 lines
4.9 KiB
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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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<TITLE>28.1.9.6. Initialize-Instance</TITLE>
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<meta name="description" value=" Initialize-Instance">
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<meta name="resource-type" value="document">
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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=tex2html5383 HREF="node299.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5381 HREF="node292.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5375 HREF="node297.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5385 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5386 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5384 HREF="node299.html"> Definitions of Make-Instance </A>
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<B>Up:</B> <A NAME=tex2html5382 HREF="node292.html"> Object Creation and </A>
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<B> Previous:</B> <A NAME=tex2html5376 HREF="node297.html"> Shared-Initialize</A>
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<HR> <P>
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<H3><A NAME=SECTION003219600000000000000>28.1.9.6. 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>initialize-instance</tt> is called by
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<tt>make-instance</tt> to initialize a newly created instance. It uses
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standard method combination. Methods for
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<tt>initialize-instance</tt> can be defined in order to perform any
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initialization that cannot be achieved with the simple slot-filling
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mechanisms.
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<P>
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<P>
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During initialization, <tt>initialize-instance</tt> is invoked
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after the following actions have been taken:
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<P>
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<UL><LI> The defaulted initialization argument list has been computed by
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combining the supplied initialization argument list with any default
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initialization arguments for the class.
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<P>
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<LI> The validity of the defaulted initialization argument
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list has been checked. If any of the initialization arguments has not
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been declared valid, an error is signaled.
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<P>
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<LI> A new instance whose slots are unbound has been created.
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<P>
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</UL>
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<P>
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The generic function <tt>initialize-instance</tt> is called with the
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new instance and the defaulted initialization arguments. There is
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a system-supplied primary method for <tt>initialize-instance</tt>
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whose parameter specializer is the class <tt>standard-object</tt>. This
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method calls the generic function <tt>shared-initialize</tt> to fill in
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the slots according to the initialization arguments and the
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<tt>:initform</tt> forms for the slots; the generic function
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<tt>shared-initialize</tt> is called with the following arguments: the instance,
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<tt>t</tt>, and the defaulted initialization arguments.
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<P>
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Note that <tt>initialize-instance</tt> provides the defaulted
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initialization argument list in its call to <tt>shared-initialize</tt>,
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so the first step performed by the system-supplied primary method for
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<tt>shared-initialize</tt> takes into account both the initialization
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arguments provided in the call to <tt>make-instance</tt> and the
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defaulted initialization argument list.
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<P>
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Methods for <tt>initialize-instance</tt> can be defined to specify
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actions to be taken when an instance is initialized. If only <tt>:after</tt>
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methods for <tt>initialize-instance</tt> are defined, they will be
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run after the system-supplied primary method for initialization and
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therefore they will not interfere with the default behavior of
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<tt>initialize-instance</tt>.
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<P>
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The Object System provides two functions that are useful in the bodies of
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<tt>initialize-instance</tt> methods. The function <tt>slot-boundp</tt>
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returns a boolean value that indicates whether a specified slot has a
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value; this provides a mechanism for writing <tt>:after</tt> methods for
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<tt>initialize-instance</tt> that initialize slots only if they have
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not already been initialized. The function <tt>slot-makunbound</tt>
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causes the slot to have no value.
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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=tex2html5383 HREF="node299.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5381 HREF="node292.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5375 HREF="node297.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5385 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5386 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5384 HREF="node299.html"> Definitions of Make-Instance </A>
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<B>Up:</B> <A NAME=tex2html5382 HREF="node292.html"> Object Creation and </A>
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<B> Previous:</B> <A NAME=tex2html5376 HREF="node297.html"> Shared-Initialize</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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