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<TITLE>CLHS: Section 7.5.2</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="07_ea.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="07_e.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="07_ec.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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7.5.2 Accessing Slots</H2> <P>
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<A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>Slots</I></A> can be <I>accessed</I> in two ways: by use of the primitive function <A REL=DEFINITION HREF="f_slt_va.htm#slot-value"><B>slot-value</B></A> and by use of <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic functions</I></A> generated by the <A REL=DEFINITION HREF="m_defcla.htm#defclass"><B>defclass</B></A> form. <P>
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The <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="f_slt_va.htm#slot-value"><B>slot-value</B></A> can be used with any of the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> names specified in the <A REL=DEFINITION HREF="m_defcla.htm#defclass"><B>defclass</B></A> form to <A REL=DEFINITION HREF="26_glo_a.htm#access"><I>access</I></A> a specific <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> <A REL=DEFINITION HREF="26_glo_a.htm#accessible"><I>accessible</I></A> in an <A REL=DEFINITION HREF="26_glo_i.htm#instance"><I>instance</I></A> of the given <A REL=DEFINITION HREF="26_glo_c.htm#class"><I>class</I></A>. <P>
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The macro <A REL=DEFINITION HREF="m_defcla.htm#defclass"><B>defclass</B></A> provides syntax for generating <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> to read and write <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A>. If a reader <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is requested, a <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is automatically generated for reading the value of the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A>, but no <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> for storing a value into it is generated. If a writer <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is requested, a <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is automatically generated for storing a value into the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A>, but no <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> for reading its value is generated. If an accessor <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is requested, a <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> for reading the value of the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> and a <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> for storing a value into the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> are automatically generated. Reader and writer <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> are implemented using <A REL=DEFINITION HREF="f_slt_va.htm#slot-value"><B>slot-value</B></A>. <P>
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When a reader or writer <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is specified for a <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A>, the name of the <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> to which the generated <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> belongs is directly specified. If the <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> specified for the writer <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is the symbol <TT>name</TT>, the <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> of the <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> for writing the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> is the symbol <TT>name</TT>, and the <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> takes two arguments: the new value and the <A REL=DEFINITION HREF="26_glo_i.htm#instance"><I>instance</I></A>, in that order. If the <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> specified for the accessor <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>method</I></A> is the symbol <TT>name</TT>, the <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> of the <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> for reading the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> is the symbol <TT>name</TT>, and the <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> of the <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> for writing the <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> is the list <TT>(setf name)</TT>. <P>
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A <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A> created or modified by supplying <TT>:reader</TT>, <TT>:writer</TT>, or <TT>:accessor</TT> <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> options can be treated exactly as an ordinary <A REL=DEFINITION HREF="26_glo_g.htm#generic_function"><I>generic function</I></A>. <P>
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Note that <A REL=DEFINITION HREF="f_slt_va.htm#slot-value"><B>slot-value</B></A> can be used to read or write the value of a <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A> whether or not reader or writer <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> exist for that <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slot</I></A>. When <A REL=DEFINITION HREF="f_slt_va.htm#slot-value"><B>slot-value</B></A> is used, no reader or writer <A REL=DEFINITION HREF="26_glo_m.htm#method"><I>methods</I></A> are invoked. <P>
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The macro <A REL=DEFINITION HREF="m_w_slts.htm#with-slots"><B>with-slots</B></A> can be used to establish a <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A> in which specified <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A> are lexically available as if they were variables. The macro <A REL=DEFINITION HREF="m_w_slts.htm#with-slots"><B>with-slots</B></A> invokes the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="f_slt_va.htm#slot-value"><B>slot-value</B></A> to <A REL=DEFINITION HREF="26_glo_a.htm#access"><I>access</I></A> the specified <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A>. <P>
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The macro <A REL=DEFINITION HREF="m_w_acce.htm#with-accessors"><B>with-accessors</B></A> can be used to establish a lexical environment in which specified <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A> are lexically available through their accessors as if they were variables. The macro <A REL=DEFINITION HREF="m_w_acce.htm#with-accessors"><B>with-accessors</B></A> invokes the appropriate accessors to <A REL=DEFINITION HREF="26_glo_a.htm#access"><I>access</I></A> the specified <A REL=DEFINITION HREF="26_glo_s.htm#slot"><I>slots</I></A>. <P>
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