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    CWG Issue 1196</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="1196"></A><H4>1196.
  
Definition required for explicit instantiation after explicit specialization?
</H4>
<B>Section: </B>13.9.3&#160; [<A href="https://wg21.link/temp.explicit">temp.explicit</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++11
 &#160;&#160;&#160;

 <B>Submitter: </B>Mike Miller
 &#160;&#160;&#160;

 <B>Date: </B>2010-09-08<BR>


<P>[Voted into the WP at the March, 2011 meeting as part of paper N3262.]</P>

<P>According to 13.9.3 [<A href="https://wg21.link/temp.explicit#4">temp.explicit</A>] paragraph 4,</P>

<BLOCKQUOTE>

For a given set of template parameters, if an explicit instantiation
of a template appears after a declaration of an explicit
specialization for that template, the explicit instantiation has no
effect.

</BLOCKQUOTE>

<P>However, that does not appear to negate the requirements of paragraph
3 that a definition of the entity being instantiated must be in scope.
Consequently, the following would appear to be ill-formed, even though
there is no real need for the definition of <TT>C</TT>:</P>

<PRE>
    template&lt;typename T&gt; class C;
    template&lt;&gt; class C&lt;int&gt; { };
    template class C&lt;int&gt;;
</PRE>

<P><B>Proposed resolution (November, 2010) [SUPERSEDED]:</B></P>

<P>Change 13.9.3 [<A href="https://wg21.link/temp.explicit">temp.explicit</A>] paragraphs 3-4 as follows:</P>

<BLOCKQUOTE>

<P>
<DEL>A declaration of a function template shall be in scope at the
point of the explicit instantiation of the function template. A
definition of the class or class template containing a member function
template shall be in scope at the point of the explicit instantiation
of the member function template. A definition of a class template or
class member template shall be in scope at the point of the explicit
instantiation of the class template or class member template.  A
definition of a class template shall be in scope at the point of an
explicit instantiation of a member function or a static data member of
the class template. A definition of a member class of a class template
shall be in scope at the point of an explicit instantiation of the
member class.</DEL> <INS>A declaration of a function template, a
member function or static data member of a class template, or a member
function template of a class or class template shall precede an
explicit instantiation of that entity. A definition of a class
template, a member class of a class template, or a member class
template of a class or class template shall precede an explicit
instantiation of that entity, unless the explicit instantiation is
preceded by an explicit specialization of the entity with the same
template arguments.</INS> If the declaration of the explicit
instantiation names an implicitly-declared special member function
(11.4.4 [<A href="https://wg21.link/special">special</A>]), the program is ill-formed.</P>

<P>For a given set of template <DEL>parameters</DEL>
<INS>arguments</INS>, if an explicit instantiation of a template
appears after a declaration of an explicit specialization for that
template, the explicit instantiation has no effect.  Otherwise...</P>

</BLOCKQUOTE>

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