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40 lines
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<TITLE>CLHS: Section 11.1.1.2.5</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="11_aabd.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="11_aab.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="11_ab.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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11.1.1.2.5 Prevention of Name Conflicts in Packages</H2> <P>
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Within one <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A>, any particular name can refer to at most one <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>. A name conflict is said to occur when there would be more than one candidate <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>. Any time a name conflict is about to occur, a <A REL=DEFINITION HREF="26_glo_c.htm#correctable"><I>correctable</I></A> <A REL=DEFINITION HREF="26_glo_e.htm#error"><I>error</I></A> is signaled. <P>
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The following rules apply to name conflicts: <P><DL><DT>-- Name conflicts are detected when they become possible, that is, when the package structure is altered. Name conflicts are not checked during every name lookup. <P><DD>
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<DT>-- If the <A REL=DEFINITION HREF="26_glo_s.htm#same"><I>same</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> is <A REL=DEFINITION HREF="26_glo_a.htm#accessible"><I>accessible</I></A> to a <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A> through more than one path, there is no name conflict. A <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> cannot conflict with itself. Name conflicts occur only between <A REL=DEFINITION HREF="26_glo_d.htm#distinct"><I>distinct</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A> with the same name (under <A REL=DEFINITION HREF="f_stgeq_.htm#stringEQ"><B>string=</B></A>). <P><DD>
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<DT>-- Every <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A> has a list of shadowing <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A>. A shadowing <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> takes precedence over any other <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> of the same name that would otherwise be <A REL=DEFINITION HREF="26_glo_a.htm#accessible"><I>accessible</I></A> in the <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A>. A name conflict involving a shadowing symbol is always resolved in favor of the shadowing <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>, without signaling an error (except for one exception involving <A REL=DEFINITION HREF="f_import.htm#import"><B>import</B></A>). See <A REL=DEFINITION HREF="f_shadow.htm#shadow"><B>shadow</B></A> and <A REL=DEFINITION HREF="f_shdw_i.htm#shadowing-import"><B>shadowing-import</B></A>. <P><DD>
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<DT>-- The functions <A REL=DEFINITION HREF="f_use_pk.htm#use-package"><B>use-package</B></A>, <A REL=DEFINITION HREF="f_import.htm#import"><B>import</B></A>, and <A REL=DEFINITION HREF="f_export.htm#export"><B>export</B></A> check for name conflicts. <P><DD>
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<DT>-- <A REL=DEFINITION HREF="f_shadow.htm#shadow"><B>shadow</B></A> and <A REL=DEFINITION HREF="f_shdw_i.htm#shadowing-import"><B>shadowing-import</B></A> never signal a name-conflict error. <P><DD>
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<DT>-- <A REL=DEFINITION HREF="f_unuse_.htm#unuse-package"><B>unuse-package</B></A> and <A REL=DEFINITION HREF="f_unexpo.htm#unexport"><B>unexport</B></A> do not need to do any name-conflict checking. <A REL=DEFINITION HREF="f_uninte.htm#unintern"><B>unintern</B></A> does name-conflict checking only when a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> being <A REL=DEFINITION HREF="26_glo_u.htm#uninterned"><I>uninterned</I></A> is a <A REL=DEFINITION HREF="26_glo_s.htm#shadowing_symbol"><I>shadowing symbol</I></A>. <P><DD>
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<DT>-- Giving a shadowing symbol to <A REL=DEFINITION HREF="f_uninte.htm#unintern"><B>unintern</B></A> can uncover a name conflict that had previously been resolved by the shadowing. <P><DD>
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<DT>-- Package functions signal name-conflict errors of <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> <A REL=DEFINITION HREF="e_pkg_er.htm#package-error"><B>package-error</B></A> before making any change to the package structure. When multiple changes are to be made, it is permissible for the implementation to process each change separately. For example, when <A REL=DEFINITION HREF="f_export.htm#export"><B>export</B></A> is given a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A>, aborting from a name conflict caused by the second <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> in the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> might still export the first <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> in the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. However, a name-conflict error caused by <A REL=DEFINITION HREF="f_export.htm#export"><B>export</B></A> of a single <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> will be signaled before that <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>'s <A REL=DEFINITION HREF="26_glo_a.htm#accessibility"><I>accessibility</I></A> in any <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A> is changed. <P><DD>
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<DT>-- Continuing from a name-conflict error must offer the user a chance to resolve the name conflict in favor of either of the candidates. The <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A> structure should be altered to reflect the resolution of the name conflict, via <A REL=DEFINITION HREF="f_shdw_i.htm#shadowing-import"><B>shadowing-import</B></A>, <A REL=DEFINITION HREF="f_uninte.htm#unintern"><B>unintern</B></A>, or <A REL=DEFINITION HREF="f_unexpo.htm#unexport"><B>unexport</B></A>. <P><DD>
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<DT>-- A name conflict in <A REL=DEFINITION HREF="f_use_pk.htm#use-package"><B>use-package</B></A> between a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> <A REL=DEFINITION HREF="26_glo_p.htm#present"><I>present</I></A> in the using <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A> and an <A REL=DEFINITION HREF="26_glo_e.htm#external_symbol"><I>external symbol</I></A> of the used <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A> is resolved in favor of the first <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> by making it a shadowing <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>, or in favor of the second <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> by uninterning the first <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> from the using <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A>. <P><DD>
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<DT>-- A name conflict in <A REL=DEFINITION HREF="f_export.htm#export"><B>export</B></A> or <A REL=DEFINITION HREF="f_uninte.htm#unintern"><B>unintern</B></A> due to a <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A>'s inheriting two <A REL=DEFINITION HREF="26_glo_d.htm#distinct"><I>distinct</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A> with the <A REL=DEFINITION HREF="26_glo_s.htm#same"><I>same</I></A> <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> (under <A REL=DEFINITION HREF="f_stgeq_.htm#stringEQ"><B>string=</B></A>) from two other <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>packages</I></A> can be resolved in favor of either <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> by importing it into the using <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A> and making it a <A REL=DEFINITION HREF="26_glo_s.htm#shadowing_symbol"><I>shadowing symbol</I></A>, just as with <A REL=DEFINITION HREF="f_use_pk.htm#use-package"><B>use-package</B></A>. <P><DD></DL><P>
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