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<TITLE>CLHS: Standard Generic Function SHARED-INITIALIZE</TITLE>
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<A NAME="shared-initialize"></I></B><I>Standard Generic Function <B>SHARED-INITIALIZE</A> <P>
<P><B>Syntax:</B><P>
<P>
<B>shared-initialize</B> <I>instance slot-names <TT>&rest</TT> initargs <TT>&key</TT> <TT>&allow-other-keys</TT></I> => <I>instance</I><P>
<P>
<P><B>Method Signatures:</B><P>
<P>
<B>shared-initialize</B> <I>(<I>instance</I><B> <A REL=DEFINITION HREF="t_std_ob.htm#standard-object">standard-object</A></B>) slot-names <TT>&rest</TT> initargs</I><P>
<P>
<P><B>Arguments and Values:</B><P>
<P>
<I>instance</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"></I><I>object</A>. <P>
<I>slot-names</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"></I><I>list</A> or <A REL=DEFINITION HREF="a_t.htm#t"></B><B>t</A>. <P>
<I>initargs</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"></I><I>list</A> of <A REL=DEFINITION HREF="26_glo_k.htm#keywordSLvalue_pair"></I><I>keyword/value pairs</A> (of initialization argument <A REL=DEFINITION HREF="26_glo_n.htm#name"></I><I>names</A> and <A REL=DEFINITION HREF="26_glo_v.htm#value"></I><I>values</A>). <P>
<P><B>Description:</B><P>
<P>
The generic function <A REL=DEFINITION HREF="#shared-initialize"></B><B>shared-initialize</A> is used to fill the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A> of an <I>instance</I> using <I>initargs</I> and <TT>:initform</TT> forms. It is called when an instance is created, when an instance is re-initialized, when an instance is updated to conform to a redefined <A REL=DEFINITION HREF="26_glo_c.htm#class"></I><I>class</A>, and when an instance is updated to conform to a different <A REL=DEFINITION HREF="26_glo_c.htm#class"></I><I>class</A>. The generic function <A REL=DEFINITION HREF="#shared-initialize"></B><B>shared-initialize</A> is called by the system-supplied primary <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> for <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"></B><B>initialize-instance</A>, <A REL=DEFINITION HREF="f_reinit.htm#reinitialize-instance"></B><B>reinitialize-instance</A>, <A REL=DEFINITION HREF="f_upda_1.htm#update-instance-for-redefined-class"></B><B>update-instance-for-redefined-class</A>, and <A REL=DEFINITION HREF="f_update.htm#update-instance-for-different-class"></B><B>update-instance-for-different-class</A>. <P>
The generic function <A REL=DEFINITION HREF="#shared-initialize"></B><B>shared-initialize</A> takes the following arguments: the <I>instance</I> to be initialized, a specification of a set of <I>slot-names</I> <A REL=DEFINITION HREF="26_glo_a.htm#accessible"></I><I>accessible</A> in that <I>instance</I>, and any number of <I>initargs</I>. The arguments after the first two must form an <A REL=DEFINITION HREF="26_glo_i.htm#initialization_argument_list"></I><I>initialization argument list</A>. The system-supplied primary <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> on <A REL=DEFINITION HREF="#shared-initialize"></B><B>shared-initialize</A> initializes the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A> with values according to the <I>initargs</I> and supplied <TT>:initform</TT> forms. <I>Slot-names</I> indicates which <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A> should be initialized according to their <TT>:initform</TT> forms if no <I>initargs</I> are provided for those <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A>. <P>
The system-supplied primary <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> behaves as follows, regardless of whether the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A> are local or shared: <P>
<P><UL><P>
<LI> If an <I>initarg</I> in the <A REL=DEFINITION HREF="26_glo_i.htm#initialization_argument_list"></I><I>initialization argument list</A> specifies a value for that <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slot</A>, that value is stored into the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slot</A>, even if a value has already been stored in the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slot</A> before the <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> is run. <P>
<LI> Any <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A> indicated by <I>slot-names</I> that are still unbound at this point are initialized according to their <TT>:initform</TT> forms. For any such <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slot</A> that has an <TT>:initform</TT> form, that <A REL=DEFINITION HREF="26_glo_f.htm#form"></I><I>form</A> is evaluated in the lexical environment of its defining <A REL=DEFINITION HREF="m_defcla.htm#defclass"></B><B>defclass</A> <A REL=DEFINITION HREF="26_glo_f.htm#form"></I><I>form</A> and the result is stored into the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slot</A>. For example, if a <A REL=DEFINITION HREF="26_glo_b.htm#before_method"></I><I>before method</A> stores a value in the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slot</A>, the <TT>:initform</TT> form will not be used to supply a value for the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slot</A>. <P>
<LI> The rules mentioned in <A REL=CHILD HREF="07_ad.htm">Section 7.1.4 (Rules for Initialization Arguments)</A> are obeyed. <P>
<P></UL><P>
The <I>slots-names</I> argument specifies the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A> that are to be initialized according to their <TT>:initform</TT> forms if no initialization arguments apply. It can be a <A REL=DEFINITION HREF="26_glo_l.htm#list"></I><I>list</A> of slot <A REL=DEFINITION HREF="26_glo_n.htm#name"></I><I>names</A>, which specifies the set of those slot <A REL=DEFINITION HREF="26_glo_n.htm#name"></I><I>names</A>; or it can be the <A REL=DEFINITION HREF="26_glo_s.htm#symbol"></I><I>symbol</A> <A REL=DEFINITION HREF="a_t.htm#t"></B><B>t</A>, which specifies the set of all of the <A REL=DEFINITION HREF="26_glo_s.htm#slot"></I><I>slots</A>. <P>
<P><B>Examples:</B> None.
<P>
<P><B>Affected By:</B> None.
<P>
<P><B>Exceptional Situations:</B> None.
<P>
<P><B>See Also:</B><P>
<P>
<A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"></B><B>initialize-instance</A>, <A REL=DEFINITION HREF="f_reinit.htm#reinitialize-instance"></B><B>reinitialize-instance</A>, <A REL=DEFINITION HREF="f_upda_1.htm#update-instance-for-redefined-class"></B><B>update-instance-for-redefined-class</A>, <A REL=DEFINITION HREF="f_update.htm#update-instance-for-different-class"></B><B>update-instance-for-different-class</A>, <A REL=DEFINITION HREF="f_slt_bo.htm#slot-boundp"></B><B>slot-boundp</A>, <A REL=DEFINITION HREF="f_slt_ma.htm#slot-makunbound"></B><B>slot-makunbound</A>, <A REL=CHILD HREF="07_a.htm">Section 7.1 (Object Creation and Initialization)</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>
<P><B>Notes:</B><P>
<P>
<I>Initargs</I> are declared as valid by using the <TT>:initarg</TT> option to <A REL=DEFINITION HREF="m_defcla.htm#defclass"></B><B>defclass</A>, or by defining <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>methods</A> for <A REL=DEFINITION HREF="#shared-initialize"></B><B>shared-initialize</A>. The keyword name of each keyword parameter specifier in the <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list"></I><I>lambda list</A> of any <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> defined on <A REL=DEFINITION HREF="#shared-initialize"></B><B>shared-initialize</A> is declared as a valid <I>initarg</I> name for all <A REL=DEFINITION HREF="26_glo_c.htm#class"></I><I>classes</A> for which that <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> is applicable. <P>
Implementations are permitted to optimize <TT>:initform</TT> forms that neither produce nor depend on side effects, by evaluating these <A REL=DEFINITION HREF="26_glo_f.htm#form"></I><I>forms</A> and storing them into slots before running any <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"></B><B>initialize-instance</A> methods, rather than by handling them in the primary <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"></B><B>initialize-instance</A> method. (This optimization might be implemented by having the <A REL=DEFINITION HREF="f_alloca.htm#allocate-instance"></B><B>allocate-instance</A> method copy a prototype instance.) <P>
Implementations are permitted to optimize default initial value forms for <I>initargs</I> associated with slots by not actually creating the complete initialization argument <A REL=DEFINITION HREF="26_glo_l.htm#list"></I><I>list</A> when the only <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> that would receive the complete <A REL=DEFINITION HREF="26_glo_l.htm#list"></I><I>list</A> is the <A REL=DEFINITION HREF="26_glo_m.htm#method"></I><I>method</A> on <A REL=DEFINITION HREF="t_std_ob.htm#standard-object"></B><B>standard-object</A>. In this case default initial value forms can be treated like <TT>:initform</TT> forms. This optimization has no visible effects other than a performance improvement. <P>
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