63 lines
6.2 KiB
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63 lines
6.2 KiB
HTML
<!-- 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: Function SLOT-BOUNDP</TITLE>
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<A NAME="slot-boundp"><I>Function</I> <B>SLOT-BOUNDP</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>slot-boundp</B> <I>instance slot-name</I> => <I>generalized-boolean</I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>instance</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<I>slot-name</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> naming a <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> of <I>instance</I>. <P>
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<I>generalized-boolean</I>---a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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Returns <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A> if the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> named <I>slot-name</I> in <I>instance</I> is bound; otherwise, returns <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A>. <P>
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<P><B>Examples:</B> None.
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<P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B><P>
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<P>
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If no <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> of the <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> <I>slot-name</I> exists in the <I>instance</I>, <A REL=DEFINITION HREF="f_slt_mi.htm#slot-missing"><B>slot-missing</B></A> is called as follows: <P>
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<PRE>
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(slot-missing (class-of instance)
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instance
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slot-name
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'slot-boundp)
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</PRE>
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</TT> <P>
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(If <A REL=DEFINITION HREF="f_slt_mi.htm#slot-missing"><B>slot-missing</B></A> is invoked and returns a value, a <A REL=DEFINITION HREF="26_glo_b.htm#boolean_equivalent"><I>boolean equivalent</I></A> to its <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A> is returned by <A REL=DEFINITION HREF="#slot-boundp"><B>slot-boundp</B></A>.) <P>
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The specific behavior depends on <I>instance</I>'s <A REL=DEFINITION HREF="26_glo_m.htm#metaclass"><I>metaclass</I></A>. An error is never signaled if <I>instance</I> has <A REL=DEFINITION HREF="26_glo_m.htm#metaclass"><I>metaclass</I></A> <A REL=DEFINITION HREF="t_std_cl.htm#standard-class"><B>standard-class</B></A>. An error is always signaled if <I>instance</I> has <A REL=DEFINITION HREF="26_glo_m.htm#metaclass"><I>metaclass</I></A> <A REL=DEFINITION HREF="t_built_.htm#built-in-class"><B>built-in-class</B></A>. The consequences are undefined if <I>instance</I> has any other <A REL=DEFINITION HREF="26_glo_m.htm#metaclass"><I>metaclass</I></A>--an error might or might not be signaled in this situation. Note in particular that the behavior for <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>conditions</I></A> and <A REL=DEFINITION HREF="26_glo_s.htm#structure"><I>structures</I></A> is not specified. <P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_slt_ma.htm#slot-makunbound"><B>slot-makunbound</B></A>, <A REL=DEFINITION HREF="f_slt_mi.htm#slot-missing"><B>slot-missing</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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The <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="#slot-boundp"><B>slot-boundp</B></A> allows for writing <A REL=DEFINITION HREF="26_glo_a.htm#after_method"><I>after methods</I></A> on <A REL=DEFINITION HREF="f_init_i.htm#initialize-instance"><B>initialize-instance</B></A> in order to initialize only those <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A> that have not already been bound. <P>
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Although no <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> is required to do so, implementors are strongly encouraged to implement the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="#slot-boundp"><B>slot-boundp</B></A> using the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <TT>slot-boundp-using-class</TT> described in the <A REL=DEFINITION HREF="26_glo_m.htm#metaobject_protocol"><I>Metaobject Protocol</I></A>. <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss320.htm">SLOT-VALUE-METACLASSES:LESS-MINIMAL</A><LI> <A REL=CHILD HREF="../Issues/iss319.htm">SLOT-MISSING-VALUES:SPECIFY</A><P></UL><HR>
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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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