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>slot-value | Common Lisp Nova Spec</TITLE
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>Common Lisp Nova Spec</A
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> <SPAN CLASS="breadcrumb-item"
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>→ <A HREF="7_Objects.html"
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>←</A
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><INPUT ID="apropos" AUTOFOCUS="AUTOFOCUS" PLACEHOLDER="Type here to search" ONINPUT="aproposInput(this);" ONKEYUP="aproposKeyup(event);" ONCHANGE="aproposChange(this);" ONFOCUS="aproposFocus(this);" ONFOCUSOUT="aproposFocusout(this);"
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><TABLE WIDTH="100%" CELLSPACING="0" CELLPADDING="0"
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><TD ALIGN="LEFT" VALIGN="BASELINE" WIDTH="100%" CLASS="name"
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><SPAN CLASS="idx" DATA-KIND="idxref" DATA-TERM="slot-value"
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></SPAN
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><B
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>slot-value</B
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></TD
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><TD ALIGN="RIGHT" VALIGN="BASELINE" WIDTH="0" NOWRAP="NOWRAP" CLASS="ftype"
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><I
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>Function</I
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></TD
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></TR
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></TABLE
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><HR
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></DIV
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><UL CLASS="subtoc"
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></UL
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><DL
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><DT
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><B
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>Syntax</B
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></DT
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><DD
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><P CLASS="j"
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><B
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>slot-value</B
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> <SPAN CLASS="cmssi"
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>object</SPAN
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> <SPAN CLASS="cmssi"
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>slot-name</SPAN
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> <SPAN CLASS="arrow"
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>→</SPAN
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> <SPAN CLASS="cmssi"
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>value</SPAN
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></P
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></DD
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><DT
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><B
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>Arguments and Values</B
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></DT
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><DD
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><P CLASS="j"
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><VAR CLASS="param"
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>object</VAR
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> — an <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>name</VAR
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> — a <A HREF="26_1_Glossary.html#symbol"
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><EM CLASS="term"
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>symbol</EM
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></A
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>. </P
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><P CLASS="j"
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><VAR CLASS="param"
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>value</VAR
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> — an <A HREF="26_1_Glossary.html#object"
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><EM CLASS="term"
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>object</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Description</B
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></DT
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><DD
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><P CLASS="j"
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>The <A HREF="26_1_Glossary.html#function"
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><EM CLASS="term"
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>function</EM
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></A
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> <A HREF="f_slot-value.html" CLASS="funref"
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><B
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>slot-value</B
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></A
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> returns the <A HREF="26_1_Glossary.html#value"
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><EM CLASS="term"
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>value</EM
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></A
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> of the <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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> named <VAR CLASS="param"
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>slot-name</VAR
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> in the <VAR CLASS="param"
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>object</VAR
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>. If there is no <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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> named <VAR CLASS="param"
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>slot-name</VAR
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>, <A HREF="f_slot-missing.html" CLASS="funref"
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><B
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>slot-missing</B
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></A
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> is called. If the <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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> is unbound, <A HREF="f_slot-unbound.html" CLASS="funref"
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><B
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>slot-unbound</B
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></A
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> is called. </P
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><P CLASS="j"
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>The macro <A HREF="f_setf.html" CLASS="macref"
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><B
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>setf</B
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></A
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> can be used with <A HREF="f_slot-value.html" CLASS="funref"
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><B
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>slot-value</B
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></A
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> to change the value of a <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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>.</P
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></DD
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><DT
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><B
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>Examples</B
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></DT
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><DD
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><PRE CLASS="screen"
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> (defclass foo ()
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((a :accessor foo-a :initarg :a :initform 1)
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(b :accessor foo-b :initarg :b)
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(c :accessor foo-c :initform 3)))
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<SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> #<STANDARD-CLASS FOO 244020371>
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(setq foo1 (make-instance 'foo :a 'one :b 'two))
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<SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> #<FOO 36325624>
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(slot-value foo1 'a) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> ONE
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(slot-value foo1 'b) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> TWO
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(slot-value foo1 'c) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> 3
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(setf (slot-value foo1 'a) 'uno) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> UNO
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(slot-value foo1 'a) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> UNO
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(defmethod foo-method ((x foo))
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(slot-value x 'a))
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<SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> #<STANDARD-METHOD FOO-METHOD (FOO) 42720573>
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(foo-method foo1) <SPAN CLASS="cmsy"
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><SPAN CLASS="arrow"
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>→</SPAN
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></SPAN
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> UNO</PRE
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></DD
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><DT
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><B
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>Exceptional Situations</B
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></DT
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><DD
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><P CLASS="j"
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>If an attempt is made to read a <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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> and no <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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> of the name <VAR CLASS="param"
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>slot-name</VAR
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> exists in the <VAR CLASS="param"
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>object</VAR
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>, <A HREF="f_slot-missing.html" CLASS="funref"
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><B
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>slot-missing</B
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></A
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> is called as follows:</P
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><PRE CLASS="screen"
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>(slot-missing (class-of <I CLASS="i"
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><I
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>instance</I
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></I
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>)
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<I CLASS="i"
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><I
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>instance</I
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></I
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>
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<I CLASS="i"
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><I
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>slot-name</I
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></I
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>
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'slot-value)</PRE
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><P CLASS="j"
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>(If <A HREF="f_slot-missing.html" CLASS="funref"
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><B
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>slot-missing</B
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></A
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> is invoked, its <A HREF="26_1_Glossary.html#primary_value"
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><EM CLASS="term"
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>primary value</EM
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></A
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> is returned by <A HREF="f_slot-value.html" CLASS="funref"
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><B
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>slot-value</B
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></A
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>.) </P
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><P CLASS="j"
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>If an attempt is made to write a <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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> and no <A HREF="26_1_Glossary.html#slot"
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><EM CLASS="term"
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>slot</EM
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></A
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> of the name <VAR CLASS="param"
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>slot-name</VAR
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> exists in the <VAR CLASS="param"
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>object</VAR
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>, <A HREF="f_slot-missing.html" CLASS="funref"
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><B
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>slot-missing</B
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></A
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> is called as follows:</P
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><PRE CLASS="screen"
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>(slot-missing (class-of <I CLASS="i"
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><I
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>instance</I
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></I
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>)
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<I CLASS="i"
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><I
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>instance</I
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></I
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>
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<I CLASS="i"
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><I
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>slot-name</I
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></I
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>
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'setf
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<I CLASS="i"
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><I
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>new-value</I
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></I
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>)</PRE
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><P CLASS="j"
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>(If <A HREF="f_slot-missing.html" CLASS="funref"
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><B
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>slot-missing</B
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></A
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> returns in this case, any <A HREF="26_1_Glossary.html#value"
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><EM CLASS="term"
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>values</EM
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></A
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> are ignored.) </P
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><P CLASS="j"
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>The specific behavior depends on <VAR CLASS="param"
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>object</VAR
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>’s <A HREF="26_1_Glossary.html#metaclass"
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><EM CLASS="term"
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>metaclass</EM
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></A
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>. An error is never signaled if <VAR CLASS="param"
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>object</VAR
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> has <A HREF="26_1_Glossary.html#metaclass"
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><EM CLASS="term"
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>metaclass</EM
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></A
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> <A HREF="t_standard-class.html" CLASS="typeref"
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><B
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>standard-class</B
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></A
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>. An error is always signaled if <VAR CLASS="param"
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>object</VAR
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> has <A HREF="26_1_Glossary.html#metaclass"
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><EM CLASS="term"
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>metaclass</EM
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></A
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> <A HREF="t_built-in-class.html" CLASS="typeref"
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><B
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>built-in-class</B
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></A
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>. The consequences are unspecified if <VAR CLASS="param"
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>object</VAR
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> has any other <A HREF="26_1_Glossary.html#metaclass"
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><EM CLASS="term"
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>metaclass</EM
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></A
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>–an error might or might not be signaled in this situation. Note in particular that the behavior for <A HREF="26_1_Glossary.html#condition"
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><EM CLASS="term"
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>conditions</EM
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></A
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> and <A HREF="26_1_Glossary.html#structure"
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><EM CLASS="term"
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>structures</EM
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></A
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> is not specified.</P
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></DD
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><DT
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><B
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>See Also</B
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></DT
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><DD
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><P CLASS="j"
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><A HREF="f_slot-missing.html" CLASS="funref"
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><B
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>slot-missing</B
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></A
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>, <A HREF="f_slot-unbound.html" CLASS="funref"
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><B
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>slot-unbound</B
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></A
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>, <A HREF="f_with-slots.html" CLASS="macref"
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><B
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>with-slots</B
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></A
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></P
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></DD
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><DT
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><B
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>Notes</B
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></DT
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><DD
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><P CLASS="j"
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>Although no <A HREF="26_1_Glossary.html#implementation"
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><EM CLASS="term"
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>implementation</EM
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></A
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> is required to do so, implementors are strongly encouraged to implement the <A HREF="26_1_Glossary.html#function"
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><EM CLASS="term"
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>function</EM
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></A
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> <A HREF="f_slot-value.html" CLASS="funref"
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><B
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>slot-value</B
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></A
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> using the <A HREF="26_1_Glossary.html#function"
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><EM CLASS="term"
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>function</EM
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></A
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> <CODE CLASS="f"
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>slot-value-using-class</CODE
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> described in the <A HREF="26_1_Glossary.html#Metaobject_Protocol"
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><EM CLASS="term"
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>Metaobject Protocol</EM
|
|
></A
|
|
>. </P
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><P CLASS="j"
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>Implementations may optimize <A HREF="f_slot-value.html" CLASS="funref"
|
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><B
|
|
>slot-value</B
|
|
></A
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> by compiling it inline.</P
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></DD
|
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></DL
|
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></DIV
|
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></DIV
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><DIV CLASS="footer"
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><DIV CLASS="btmnav"
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><A HREF="f_slot-unbound.html" CLASS="prev"
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>←</A
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><A HREF="f_method-qualifiers.html" CLASS="next"
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>→</A
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>Conversion to HTML copyright 2023 by Gilbert Baumann</DIV
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