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[class.mem.general] Allow non-defining declarations of nested classes. #4416

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[class.mem.general] Allow non-defining declarations of nested classes. #4416

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18 changes: 13 additions & 5 deletions source/classes.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -666,11 +666,19 @@
and conversion function declarations only;
when declaring another kind of member the \grammarterm{decl-specifier-seq}
shall contain a \grammarterm{type-specifier} that is not a \grammarterm{cv-qualifier}.
The
\grammarterm{member-declarator-list} can be omitted only after a
\grammarterm{class-specifier} or an \grammarterm{enum-specifier} or in a
friend declaration\iref{class.friend}. A
\grammarterm{pure-specifier} shall be used only in the declaration of a
The \grammarterm{member-declarator-list} can be omitted only
after
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I think "can be omitted only after" is problematic phrasing -- it's unclear whether it's giving permission, stating a restriction, or both. (Can a member-declarator-list be omitted after any elaborated-type-specifier, or only some of them?) This is made a little worse by this change, because three of the four top-level grammar productions for elaborated-type-specifier aren't allowed in this context, per the end of [dcl.type.elab]p1. This might help:

The \grammarterm{member-declarator-list} shall not be omitted unless
the declaration is a friend declaration or its sole constituent is

  • ...

\begin{itemize}
\item
a \grammarterm{class-specifier},
\item
an \grammarterm{enum-specifier}, or
\item
an \grammarterm{elaborated-type-specifier}
that is the sole constituent of a declaration\iref{dcl.type.elab}, or
\end{itemize}
in a friend declaration\iref{class.friend}.
A \grammarterm{pure-specifier} shall be used only in the declaration of a
virtual function\iref{class.virtual}
that is not a friend declaration.

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