[CWG 2026-06-19] P3670R4 Pack Indexing for Template Names

source/basic.tex

@@ -2174,7 +2174,7 @@
 rules apply.
 In some cases
 a name followed by \tcode{<} is treated as a \grammarterm{template-name}
-even though name lookup did not find a \grammarterm{template-name}
+even though name lookup did not find the declaration of a template
 (see \ref{temp.names}).
 For example,
 \begin{codeblock}

source/declarations.tex

@@ -1368,7 +1368,8 @@
     nested-name-specifier \keyword{template} simple-template-id\br
     computed-type-specifier\br
     placeholder-type-specifier\br
-    \opt{nested-name-specifier} template-name\br
+    \opt{nested-name-specifier} simple-template-name\br
+    pack-index-template-name\br
     \keyword{char}\br
     \keyword{char8_t}\br
     \keyword{char16_t}\br
@@ -1405,7 +1406,7 @@
 \grammarterm{nested-name-specifier},
 \grammarterm{type-name},
 \grammarterm{simple-template-id},
-\grammarterm{template-name}, and/or
+\grammarterm{simple-template-name}, and/or
 \grammarterm{type-constraint}
 (if it is a \grammarterm{placeholder-type-specifier}).
 The component name of a \grammarterm{type-name} is the first name in it.
@@ -1432,19 +1433,24 @@
 a type to be deduced\iref{dcl.spec.auto}.
 \indextext{deduction!class template arguments}%
 A \grammarterm{type-specifier} is a placeholder for
-a deduced class type\iref{dcl.type.class.deduct} if either
+a deduced class type\iref{dcl.type.class.deduct} if
 \begin{itemize}
 \item
 it is of the form
-\opt{\keyword{typename}} \opt{\grammarterm{nested-name-specifier}} \grammarterm{template-name} or
+\opt{\keyword{typename}} \opt{\grammarterm{nested-name-specifier}} \grammarterm{simple-template-name}, or
+\item
+it is of the form
+\opt{\keyword{typename}} \grammarterm{pack-index-template-name}, or
 \item
 it is of the form \opt{\keyword{typename}} \grammarterm{splice-specifier} and
 the \grammarterm{splice-specifier} designates
 a class template or alias template.
 \end{itemize}
 The \grammarterm{nested-name-specifier} or \grammarterm{splice-specifier},
-if any, shall be non-dependent and
-the \grammarterm{template-name} or \grammarterm{splice-specifier}
+if any, shall be non-dependent and the
+\grammarterm{simple-template-name},
+\grammarterm{pack-index-template-name}, or
+\grammarterm{splice-specifier}
 shall designate a deducible template.
 A \defnadj{deducible}{template} is
 \begin{itemize}

source/grammar.tex

@@ -54,7 +54,7 @@
 \end{ncbnf}
 
 \begin{ncbnf}
-template-name:\br
+simple-template-name:\br
 	identifier
 \end{ncbnf}
 

source/preprocessor.tex

@@ -2426,7 +2426,7 @@
 \defnxname{cpp_nontype_template_args}             & \tcode{201911L} \\ \rowsep
 \defnxname{cpp_nontype_template_parameter_auto}   & \tcode{201606L} \\ \rowsep
 \defnxname{cpp_nsdmi}                             & \tcode{200809L} \\ \rowsep
-\defnxname{cpp_pack_indexing}                     & \tcode{202311L} \\ \rowsep
+\defnxname{cpp_pack_indexing}                     & \tcode{202606L} \\ \rowsep
 \defnxname{cpp_placeholder_variables}             & \tcode{202306L} \\ \rowsep
 \defnxname{cpp_pp_embed}                          & \tcode{202502L} \\ \rowsep
 \defnxname{cpp_range_based_for}                   & \tcode{202211L} \\ \rowsep

source/templates.tex

@@ -733,6 +733,17 @@
 
 \begin{bnf}
 \nontermdef{template-name}\br
+  simple-template-name\br
+  pack-index-template-name
+\end{bnf}
+
+\begin{bnf}
+\nontermdef{pack-index-template-name}\br
+  simple-template-name \terminal{...} \terminal{[} constant-expression \terminal{]}\br
+\end{bnf}
+
+\begin{bnf}
+\nontermdef{simple-template-name}\br
   identifier
 \end{bnf}
 
@@ -764,10 +775,32 @@
 \grammarterm{template-name}
 is the first name in it.
 
+\pnum
+The \grammarterm{simple-template-name} $P$
+in a \grammarterm{pack-index-template-name}
+shall denote a pack.
+
+\pnum
+The \grammarterm{constant-expression}
+shall be a converted constant expression\iref{expr.const.const}
+of type \tcode{std::size_t}
+whose value $V$, termed the index, is such that
+$0 \le V < \tcode{sizeof...(}P\tcode{)}$.
+
+\pnum
+A \grammarterm{pack-index-template-name}
+is a pack expansion\iref{temp.variadic}.
+
+\pnum
+\begin{note}
+The \grammarterm{pack-index-template-name}
+denotes the $V^\text{th}$ \grammarterm{template-name} of the pack.
+\end{note}
+
 \pnum
 A \tcode{<} is interpreted as the delimiter of
 a \grammarterm{template-argument-list}
-if either
+if
 \begin{itemize}
 \item
 it follows a \grammarterm{splice-specifier} that either
@@ -776,6 +809,8 @@
 \item is preceded by \keyword{template} or \keyword{typename}, or
 \end{itemize}
 \item
+it follows a \grammarterm{pack-index-template-name}, or
+\item
 it follows a name that is not a \grammarterm{conversion-function-id} and
 \begin{itemize}
 \item
@@ -2660,6 +2695,20 @@
 Otherwise, two such \grammarterm{pack-index-specifier}s refer to the same type
 only if their indexes have the same value.
 
+\pnum
+Two \grammarterm{pack-index-template-name}{s}
+refer to the same template only if
+\begin{itemize}
+\item
+their \grammarterm{simple-template-name}{s}
+refer to the same template parameter pack and
+\item
+if neither of their \grammarterm{constant-expression}{s} is value-dependent,
+then they have the same value,
+otherwise their \grammarterm{constant-expression}{s}
+are equivalent\iref{temp.over.link}.
+\end{itemize}
+
 \rSec1[temp.decls]{Template declarations}
 
 \rSec2[temp.decls.general]{General}
@@ -2906,7 +2955,7 @@
 
 \begin{bnf}
 \nontermdef{deduction-guide}\br
-    \opt{explicit-specifier} template-name \terminal{(} parameter-declaration-clause \terminal{)} \terminal{->} simple-template-id \opt{requires-clause} \terminal{;}
+    \opt{explicit-specifier} simple-template-name \terminal{(} parameter-declaration-clause \terminal{)} \terminal{->} simple-template-id \opt{requires-clause} \terminal{;}
 \end{bnf}
 
 \pnum
@@ -2937,7 +2986,7 @@
 a deduction guide.
 The \grammarterm{simple-template-id}
 shall name a class template specialization.
-The \grammarterm{template-name}
+The \grammarterm{simple-template-name}
 shall be the same \grammarterm{identifier}
 as the \grammarterm{template-name}
 of the \grammarterm{simple-template-id}.
@@ -3300,6 +3349,9 @@
 \item In a \grammarterm{pack-index-specifier};
 the pattern is a \grammarterm{typedef-name}.
 
+\item In a \grammarterm{pack-index-template-name};
+the pattern is a \grammarterm{simple-template-name}.
+
 \item In a \grammarterm{fold-expression}\iref{expr.prim.fold};
 the pattern is the \grammarterm{cast-expression}
 that contains an unexpanded pack.
@@ -3425,6 +3477,11 @@
 let $K$ be the index of $P$.
 The instantiation of $P$ is the \grammarterm{typedef-name} $\tcode{E}_K$.
 
+\pnum
+When instantiating a \grammarterm{pack-index-template-name} $P$,
+let $K$ be the index of $P$.
+The instantiation of $P$ is the \grammarterm{simple-template-name} $\tcode{E}_K$.
+
 \pnum
 The instantiation of an \grammarterm{alignment-specifier} with an ellipsis
 produces $\tcode{E}_1$ $\tcode{E}_2$ $\dotsc$ $\tcode{E}_N$.
@@ -4675,7 +4732,7 @@
 \grammarterm{alias-declaration}\iref{dcl.pre} declares the
 \grammarterm{identifier} to be an \defnadj{alias}{template}.
 An alias template is a name for a family of
-types. The name of the alias template is a \grammarterm{template-name}.
+types. The name of the alias template is a \grammarterm{simple-template-name}.
 
 \pnum
 A