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[expr.type.conv] Move description of 'auto' deduction to [dcl.type.auto.deduct] #5039

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Oct 21, 2021
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[expr.type.conv] Move description of 'auto' deduction to [dcl.type.auto.deduct] #5039

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14 changes: 14 additions & 0 deletions source/declarations.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -1950,6 +1950,20 @@
and $E$ is the \grammarterm{assignment-expression}.
\end{itemize}
\item
For an explicit type conversion\iref{expr.type.conv},
\tcode{T} is the specified type, which shall be \keyword{auto}.
\begin{itemize}
\item
If the initializer is a \grammarterm{braced-init-list},
it shall consist of a single brace-enclosed \grammarterm{assignment-expression}
and $E$ is the \grammarterm{assignment-expression}.
\item
If the initializer is a parenthesized \grammarterm{expression-list},
the \grammarterm{expression-list} shall be
a single \grammarterm{assignment-expression}
and $E$ is the \grammarterm{assignment-expression}.
Comment on lines +1961 to +1964
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It's weird to say this explicitly for auto(4) but not for auto x(4);, since the latter's initializer is (4). It's preexisting, but should we adjust /2.2 (or even try to combine them)?

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But... we say that in p2.2.3:

If the initializer is a parenthesized expression-list, the expression-list shall be a single assignment-expression and E is the assignment-expression

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I'd say let's leave this for now? I'm not sure what exactly we could improve here.

\end{itemize}
\item
For a non-type template parameter declared with a type
that contains a placeholder type,
\tcode{T} is the declared type of the non-type template parameter
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11 changes: 3 additions & 8 deletions source/expressions.tex
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Expand Up @@ -3353,14 +3353,9 @@
of the function selected by overload resolution
for class template deduction\iref{over.match.class.deduct}
for the remainder of this subclause.
Otherwise, if the type is \tcode{auto},
it is replaced by the type deduced for the variable \tcode{x}
in the invented declaration\iref{dcl.spec.auto},
which is never interpreted as a function declaration:
\begin{codeblock}
auto x @\placeholder{init}@;
\end{codeblock}
, where \placeholder{init} is the initializer.
Otherwise, if the type contains a placeholder type,
it is replaced by the type
determined by placeholder type deduction\iref{dcl.type.auto.deduct}.
\begin{example}
\begin{codeblock}
struct A {};
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