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91 lines
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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>28.1.9.5. Shared-Initialize</TITLE>
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<meta name="description" value=" Shared-Initialize">
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html5371 HREF="node298.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5369 HREF="node292.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5363 HREF="node296.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5373 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5374 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5372 HREF="node298.html"> Initialize-Instance</A>
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<B>Up:</B> <A NAME=tex2html5370 HREF="node292.html"> Object Creation and </A>
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<B> Previous:</B> <A NAME=tex2html5364 HREF="node296.html"> Rules for Initialization </A>
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<HR> <P>
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<H3><A NAME=SECTION003219500000000000000>28.1.9.5. Shared-Initialize</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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<A NAME=SharedInitializeSECTION>The</A>
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generic function <tt>shared-initialize</tt> is used to fill the slots
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of an instance using initialization arguments and <tt>:initform</tt>
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forms when an instance is created, when an instance is re-initialized,
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when an instance is updated to conform to a redefined class, and when
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an instance is updated to conform to a different class. It uses
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standard method combination. It takes the following arguments: the
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instance to be initialized, a specification of a set of names of slots
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accessible in that instance, and any number of initialization
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arguments. The arguments after the first two must form an initialization
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argument list.
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<P>
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The second argument to <tt>shared-initialize</tt> may be one of the following:
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<P>
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<UL><LI> It can be a list of slot names, which specifies
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the set of those slot names.
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<P>
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<LI> It can be <tt>nil</tt>, which specifies the empty set of
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slot names.
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<P>
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<LI> It can be the symbol <tt>t</tt>, which specifies the set of
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all of the slots.
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<P>
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</UL>
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<P>
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There is a system-supplied primary method for
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<tt>shared-initialize</tt> whose first parameter specializer is the class
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<tt>standard-object</tt>. This method behaves as follows on each slot,
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whether shared or local:
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<P>
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<UL><LI> If an initialization argument in the initialization
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argument list specifies a value for that slot, that value is stored
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into the slot, even if a value has already been stored in the slot
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before the method is run. The affected slots are independent of which
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slots are indicated by the second argument to <tt>shared-initialize</tt>.
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<P>
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<LI> Any slots indicated by the second argument that are still
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unbound at this point are initialized according to their
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<tt>:initform</tt> forms. For any such slot that has an <tt>:initform</tt> form,
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that form is evaluated in the lexical environment of its defining
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<tt>defclass</tt> form and the result is stored into the slot. For example,
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if a <tt>:before</tt> method stores a value in the slot, the
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<tt>:initform</tt> form will not be used to supply a value for the slot. If
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the second argument specifies a name that does not correspond to any
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slots accessible in the instance, the results are unspecified.
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<P>
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<LI> The rules mentioned in section <A HREF="node296.html#RulesforInitializationArgumentsSECTION">28.1.9.4</A> are obeyed.
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<P>
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</UL>
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<P>
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The generic function <tt>shared-initialize</tt> is called by the
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system-supplied primary methods for the generic functions
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<tt>initialize-instance</tt>,
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<tt>reinitialize-instance</tt>,
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<tt>update-instance-for-different-class</tt>, and
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<tt>update-instance-for-redefined-class</tt>.
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Thus methods can be written for
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<tt>shared-initialize</tt> to specify actions that should be taken in all of
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these contexts.
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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=tex2html5371 HREF="node298.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html5369 HREF="node292.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html5363 HREF="node296.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html5373 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html5374 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html5372 HREF="node298.html"> Initialize-Instance</A>
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<B>Up:</B> <A NAME=tex2html5370 HREF="node292.html"> Object Creation and </A>
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<B> Previous:</B> <A NAME=tex2html5364 HREF="node296.html"> Rules for Initialization </A>
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<HR> <P>
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