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34 lines
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<TITLE>CLHS: Section 15.1.2.1</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="15_ab.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="15_ab.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="15_abb.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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15.1.2.1 Array Upgrading</H2> <P>
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<P>
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The <A REL=DEFINITION HREF="26_glo_u.htm#upgraded_array_element_type"><I>upgraded array element type</I></A> of a <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> T1 is a <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> T2 that is a <A REL=DEFINITION HREF="26_glo_s.htm#supertype"><I>supertype</I></A> of T1 and that is used instead of T1 whenever T1 is used as an <A REL=DEFINITION HREF="26_glo_a.htm#array_element_type"><I>array element type</I></A> for object creation or type discrimination. <P>
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During creation of an <A REL=DEFINITION HREF="26_glo_a.htm#array"><I>array</I></A>, the <A REL=DEFINITION HREF="26_glo_e.htm#element_type"><I>element type</I></A> that was requested is called the <A REL=DEFINITION HREF="26_glo_e.htm#expressed_array_element_type"><I>expressed array element type</I></A>. The <A REL=DEFINITION HREF="26_glo_u.htm#upgraded_array_element_type"><I>upgraded array element type</I></A> of the <A REL=DEFINITION HREF="26_glo_e.htm#expressed_array_element_type"><I>expressed array element type</I></A> becomes the <A REL=DEFINITION HREF="26_glo_a.htm#actual_array_element_type"><I>actual array element type</I></A> of the <A REL=DEFINITION HREF="26_glo_a.htm#array"><I>array</I></A> that is created. <P>
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<A REL=DEFINITION HREF="26_glo_t.htm#type"><I>Type</I></A> <I>upgrading</I> implies a movement upwards in the type hierarchy lattice. A <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> is always a <A REL=DEFINITION HREF="26_glo_s.htm#subtype"><I>subtype</I></A> of its <A REL=DEFINITION HREF="26_glo_u.htm#upgraded_array_element_type"><I>upgraded array element type</I></A>. Also, if a <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> Tx is a <A REL=DEFINITION HREF="26_glo_s.htm#subtype"><I>subtype</I></A> of another <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> Ty, then the <A REL=DEFINITION HREF="26_glo_u.htm#upgraded_array_element_type"><I>upgraded array element type</I></A> of Tx must be a <A REL=DEFINITION HREF="26_glo_s.htm#subtype"><I>subtype</I></A> of the <A REL=DEFINITION HREF="26_glo_u.htm#upgraded_array_element_type"><I>upgraded array element type</I></A> of Ty. Two <A REL=DEFINITION HREF="26_glo_d.htm#disjoint"><I>disjoint</I></A> <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>types</I></A> can be <I>upgraded</I> to the same <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A>. <P>
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The <A REL=DEFINITION HREF="26_glo_u.htm#upgraded_array_element_type"><I>upgraded array element type</I></A> T2 of a <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> T1 is a function only of T1 itself; that is, it is independent of any other property of the <A REL=DEFINITION HREF="26_glo_a.htm#array"><I>array</I></A> for which T2 will be used, such as <A REL=DEFINITION HREF="26_glo_r.htm#rank"><I>rank</I></A>, <A REL=DEFINITION HREF="26_glo_a.htm#adjustability"><I>adjustability</I></A>, <A REL=DEFINITION HREF="26_glo_f.htm#fill_pointer"><I>fill pointers</I></A>, or displacement. The <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="f_upgr_1.htm#upgraded-array-element-type"><B>upgraded-array-element-type</B></A> can be used by <A REL=DEFINITION HREF="26_glo_c.htm#conforming_program"><I>conforming programs</I></A> to predict how the <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> will <A REL=DEFINITION HREF="26_glo_u.htm#upgrade"><I>upgrade</I></A> a given <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A>. <P>
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<P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issue</A>, <I>not part of the specification</I>, applies to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss015.htm">ARRAY-TYPE-ELEMENT-TYPE-SEMANTICS:UNIFY-UPGRADING</A><P></UL><HR>
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