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<H1> 4.9.1 Statically Matching Constraints and Subtypes</H1>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2878"></A>A constraint <I>statically
matches</I> another constraint if both are null constraints, both are
static and have equal corresponding bounds or discriminant values, or
both are nonstatic and result from the same elaboration of a <FONT FACE="Arial, Helvetica">constraint</FONT>
of a <FONT FACE="Arial, Helvetica">subtype_indication</FONT> or the same
evaluation of a <FONT FACE="Arial, Helvetica">range</FONT> of a <FONT FACE="Arial, Helvetica">discrete_subtype_definition</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2879"></A>A subtype <I>statically matches</I>
another subtype of the same type if they have statically matching constraints.
Two anonymous access subtypes statically match if their designated subtypes
statically match. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>Statically
matching constraints and subtypes are the basis for subtype conformance
of profiles (see <A HREF="AA-6-3-1.html">6.3.1</A>). </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2880"></A>Two ranges of the same type
<I>statically match</I> if both result from the same evaluation of a
<FONT FACE="Arial, Helvetica">range</FONT>, or if both are static and
have equal corresponding bounds. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>The notion
of static matching of ranges is used in <A HREF="AA-12-5-3.html">12.5.3</A>,
``<A HREF="AA-12-5-3.html">Formal Array Types</A>''; the index ranges
of formal and actual constrained array subtypes have to statically match.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2881"></A>A constraint is <I>statically
compatible</I> with a scalar subtype if it statically matches the constraint
of the subtype, or if both are static and the constraint is compatible
with the subtype. <A NAME="I2882"></A>A constraint is <I>statically compatible</I>
with an access or composite subtype if it statically matches the constraint
of the subtype, or if the subtype is unconstrained. <A NAME="I2883"></A>One
subtype is <I>statically compatible</I> with a second subtype if the
constraint of the first is statically compatible with the second subtype.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>Static compatibility
is required when constraining a parent subtype with a discriminant from
a new <FONT FACE="Arial, Helvetica">discriminant_part</FONT>. See <A HREF="AA-3-7.html">3.7</A>.
Static compatibility is also used in matching generic formal derived
types.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Note that statically compatible
with a subtype does not imply compatible with a type. It is OK since
the terms are used in different contexts. </FONT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>This subclause is new to Ada 95.
</FONT></DIV>
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