Merge 2022-11 CWG Motion 3

P2710R0 Core Language Working Group NB comment resolutions for the November, 2022 meeting;
excluding  issues 2615, 2639, 2640, 2652, 2653, 2654, and 2538

After consultation with CWG, the resolution for CWG2642 was not applied
and has been returned to CWG for reconsideration.

Author: tkoeppe

source/basic.tex

@@ -675,6 +675,11 @@
 \item In each such definition, corresponding entities shall have the
 same language linkage.
 
+\item In each such definition,
+const objects with static or thread storage duration
+shall be constant-initialized if
+the object is constant-initialized in any such definition.
+
 \item In each such definition, the overloaded operators referred
 to, the implicit calls to conversion functions, constructors, operator
 new functions and operator delete functions, shall refer to the same
@@ -4661,9 +4666,14 @@
 can be an array of unknown bound and therefore be incomplete at one
 point in a translation unit and complete later on; the array types at
 those two points (``array of unknown bound of \tcode{T}'' and ``array of
-\tcode{N} \tcode{T}'') are different types. The type of a pointer to array of
-unknown bound, or of a type defined by a \keyword{typedef} declaration to
-be an array of unknown bound, cannot be completed.
+\tcode{N} \tcode{T}'') are different types.
+\begin{note}
+The type of a pointer or reference to array of unknown bound
+permanently points to or refers to an incomplete type.
+An array of unknown bound named by a \keyword{typedef} declaration
+permanently refers to an incomplete type.
+In either case, the array type cannot be completed.
+\end{note}
 \begin{example}
 \indextext{type!example of incomplete}%
 \begin{codeblock}
@@ -5580,6 +5590,10 @@
 \item
 The constituent expression of an expression is that expression.
 \item
+The constituent expression of a conversion is
+the corresponding implicit function call, if any, or
+the converted expression otherwise.
+\item
 The constituent expressions of a \grammarterm{braced-init-list} or
 of a (possibly parenthesized) \grammarterm{expression-list}
 are the constituent expressions of the elements of the respective list.
@@ -5627,6 +5641,15 @@
 Expressions appearing in the \grammarterm{compound-statement} of a \grammarterm{lambda-expression}
 are not subexpressions of the \grammarterm{lambda-expression}.
 \end{note}
+The \defnadjx{potentially-evaluated}{subexpressions}{subexpression} of
+an expression, conversion, or \grammarterm{initializer} $E$ are
+\begin{itemize}
+\item
+the constituent expressions of $E$ and
+\item
+the subexpressions thereof that
+are not subexpressions of a nested unevaluated operand\iref{term.unevaluated.operand}.
+\end{itemize}
 
 \pnum
 A \defn{full-expression} is

source/classes.tex

@@ -659,6 +659,11 @@
 shall not directly or indirectly cause the implicit definition of a
 defaulted default constructor for the enclosing class or the
 exception specification of that constructor.
+An immediate invocation\iref{expr.const} that
+is a potentially-evaluated subexpression\iref{intro.execution}
+of a default member initializer
+is neither evaluated nor checked for whether it
+is a constant expression at the point where the subexpression appears.
 
 \pnum
 A member shall not be declared with the \keyword{extern}

source/declarations.tex

@@ -1356,11 +1356,6 @@
     class-key \opt{attribute-specifier-seq} \opt{nested-name-specifier} identifier\br
     class-key simple-template-id\br
     class-key nested-name-specifier \opt{\keyword{template}} simple-template-id\br
-    elaborated-enum-specifier
-\end{bnf}
-
-\begin{bnf}
-\nontermdef{elaborated-enum-specifier}\br
     \keyword{enum} \opt{nested-name-specifier} identifier
 \end{bnf}
 
@@ -4009,7 +4004,12 @@
 copy-initialization semantics\iref{dcl.init}.
 The names in the
 default argument are looked up, and the semantic constraints are checked,
-at the point where the default argument appears.
+at the point where the default argument appears, except that
+an immediate invocation\iref{expr.const} that
+is a potentially-evaluated subexpression\iref{intro.execution} of
+the \grammarterm{initializer-clause} in a \grammarterm{parameter-declaration} is
+neither evaluated
+nor checked for whether it is a constant expression at that point.
 Name lookup and checking of semantic constraints for default
 arguments of templated functions are performed as described in~\ref{temp.inst}.
 \begin{example}
@@ -4689,6 +4689,14 @@
 \end{note}
 \end{itemize}
 
+\pnum
+An immediate invocation\iref{expr.const} that is not evaluated where
+it appears\iref{dcl.fct.default,class.mem.general}
+is evaluated and checked for whether it is
+a constant expression at the point where
+the enclosing \grammarterm{initializer} is used in
+a function call, a constructor definition, or an aggregate initialization.
+
 \pnum
 An \grammarterm{initializer-clause} followed by an ellipsis is a
 pack expansion\iref{temp.variadic}.
@@ -6192,35 +6200,33 @@
 
 \pnum
 An explicitly defaulted special member function $\tcode{F}_1$
-with type $\tcode{T}_1$
 is allowed to differ from
 the corresponding special member function $\tcode{F}_2$
-with type $\tcode{T}_2$
 that would have been implicitly declared, as follows:
 \begin{itemize}
 \item
-  $\tcode{T}_1$ and $\tcode{T}_2$ may have differing \grammarterm{ref-qualifier}{s};
+  $\tcode{F}_1$ and $\tcode{F}_2$ may have differing \grammarterm{ref-qualifier}{s};
 \item
   if $\tcode{F}_2$ has an implicit object parameter of
   type ``reference to \tcode{C}'',
   $\tcode{F}_1$ may be an explicit object member function whose
   explicit object parameter is of type ``reference to \tcode{C}'',
-  in which case $\tcode{T}_1$ would differ from $\tcode{T}_2$
-  in that $\tcode{T}_1$ has an additional parameter;
+  in which case the type of $\tcode{F}_1$ would differ from the type of $\tcode{F}_2$
+  in that the type of $\tcode{F}_1$ has an additional parameter;
 \item
-  $\tcode{T}_1$ and $\tcode{T}_2$ may have differing exception specifications; and
+  $\tcode{F}_1$ and $\tcode{F}_2$ may have differing exception specifications; and
 \item
   if $\tcode{F}_2$ has a non-object parameter of type \tcode{const C\&},
   the corresponding non-object parameter of $\tcode{F}_1$ may be of
   type \tcode{C\&}.
 \end{itemize}
-If $\tcode{T}_1$ differs from $\tcode{T}_2$ in a way
+If the type of $\tcode{F}_1$ differs from the type of $\tcode{F}_2$ in a way
 other than as allowed by the preceding rules, then:
 \begin{itemize}
 \item
   if $\tcode{F}_1$ is an assignment operator, and
-  the return type of $\tcode{T}_1$ differs from
-  the return type of $\tcode{T}_2$ or
+  the return type of $\tcode{F}_1$ differs from
+  the return type of $\tcode{F}_2$ or
   $\tcode{F}_1${'s} non-object parameter type is not a reference,
   the program is ill-formed;
 \item
@@ -7161,13 +7167,23 @@
 
 \begin{bnf}
 \nontermdef{using-enum-declaration}\br
-    \terminal{using} elaborated-enum-specifier \terminal{;}
+    \keyword{using} \keyword{enum} using-enum-declarator \terminal{;}
+\end{bnf}
+
+\begin{bnf}
+\nontermdef{using-enum-declarator}\br
+    \opt{nested-name-specifier} identifier\br
+    \opt{nested-name-specifier} simple-template-id
 \end{bnf}
 
 \pnum
-The \grammarterm{elaborated-enum-specifier}
-shall not name a dependent type
-and the type shall have a reachable \grammarterm{enum-specifier}.
+A \grammarterm{using-enum-declarator}
+names the set of declarations found by
+lookup\iref{basic.lookup.unqual,basic.lookup.qual}
+for the \grammarterm{using-enum-declarator}.
+The \grammarterm{using-enum-declarator}
+shall designate a non-dependent type
+with a reachable \grammarterm{enum-specifier}.
 
 \pnum
 A \grammarterm{using-enum-declaration}

source/expressions.tex

@@ -2358,7 +2358,7 @@
             return x+2;
          }();                               // Updates \tcode{::x} to 6, and initializes \tcode{y} to 7.
 
-auto z = [a = 42](int a) { return 1; };     // error: parameter and local variable have the same name
+auto z = [a = 42](int a) { return 1; };     // error: parameter and conceptual local variable have the same name
 auto counter = [i=0]() mutable -> decltype(i) {     // OK, returns \tcode{int}
   return i++;
 };
@@ -7326,7 +7326,7 @@
 \pnum
 A variable is \defn{potentially-constant} if
 it is constexpr or
-it has reference or const-qualified integral or enumeration type.
+it has reference or non-volatile const-qualified integral or enumeration type.
 
 \pnum
 A constant-initialized potentially-constant variable $V$ is
@@ -7923,8 +7923,7 @@
 or
 
 \item
-a subexpression of one of the above
-that is not a subexpression of a nested unevaluated operand\iref{term.unevaluated.operand}.
+a potentially-evaluated subexpression\iref{intro.execution} of one of the above.
 \end{itemize}
 
 \indextext{function!needed for constant evaluation}%
@@ -7938,9 +7937,7 @@
 that is potentially constant evaluated, or
 
 \item
-a variable named by a potentially constant evaluated expression
-that is either a constexpr variable or
-is of non-volatile const-qualified integral type or of reference type.
+a potentially-constant variable named by a potentially constant evaluated expression.
 \end{itemize}
 
 \indextext{expression|)}

source/overloading.tex

@@ -579,12 +579,6 @@
 When comparing the call against a
 surrogate call function, the implied object argument is compared
 against the first parameter of the surrogate call function.
-The
-conversion function from which the surrogate call function was
-derived will be used in the conversion sequence for that
-parameter since it converts the implied object argument to the
-appropriate function pointer or reference required by that first
-parameter.
 \end{note}
 \begin{example}
 \begin{codeblock}
@@ -3418,11 +3412,12 @@
 where the \grammarterm{postfix-expression} is of class type,
 the operator function
 is selected by overload resolution\iref{over.call.object}.
-If a surrogate call function for a conversion function
-named \keyword{operator} \grammarterm{conversion-type-id} is selected,
+If a surrogate call function is selected,
+let $e$ be the result of invoking the corresponding conversion operator function on the \grammarterm{postfix-expression};
+
 the expression is interpreted as
 \begin{ncsimplebnf}
-postfix-expression \terminal{.} \keyword{operator} conversion-type-id \terminal{(}\terminal{)} \terminal{(} \opt{expression-list} \terminal{)}
+$e$ \terminal{(} \opt{expression-list} \terminal{)}
 \end{ncsimplebnf}
 Otherwise, the expression is interpreted as
 \begin{ncsimplebnf}

source/support.tex

@@ -5783,6 +5783,11 @@
 \pnum
 The contents of the header \libheaderdef{cstdarg} are the same as the C
 standard library header \libheader{stdarg.h}, with the following changes:
+\begin{itemize}
+\item
+In lieu of the default argument promotions specified in ISO C 6.5.2.2,
+the definition in~\ref{expr.call} applies.
+\item
 The restrictions that ISO C places on the second parameter to the
 \indexlibraryglobal{va_start}%
 \tcode{va_start} macro in header \libheader{stdarg.h}
@@ -5808,6 +5813,7 @@
 is of a reference type, or of a type that is not compatible with the
 type that results when passing an argument for which there is no
 parameter, the behavior is undefined.
+\end{itemize}
 
 \xrefc{7.16.1.1}
 

source/templates.tex

@@ -5978,13 +5978,17 @@
 It is unspecified whether or not an implementation implicitly instantiates a
 virtual member function of a class template if the virtual member function would
 not otherwise be instantiated.
-The use of a template specialization in a default argument
-shall not cause the template to be implicitly instantiated except that a
-class template may be instantiated where its complete type is needed to determine
-the correctness of the default argument.
+The use of a template specialization in
+a default argument or default member initializer
+shall not cause the template to be implicitly instantiated except
+where needed to determine
+the correctness of the default argument or default member initializer.
 The use of a default argument in a
 function call causes specializations in the default argument to be implicitly
 instantiated.
+Similarly, the use of a default member initializer
+in a constructor definition or an aggregate initialization
+causes specializations in the default member initializer to be instantiated.
 
 \pnum
 If a function template
@@ -7325,9 +7329,11 @@
 \begin{example}
 \begin{codeblock}
 template <class T, T> struct S {};
-template <class T> int f(S<T, T()>*);
-struct X {};
-int i0 = f<X>(0);
+template <class T> int f(S<T, T{}>*);   // \#1
+class X {
+  int m;
+};
+int i0 = f<X>(0);   // \#1 uses a value of non-structural type \tcode{X} as a non-type template argument
 \end{codeblock}
 \end{example}
 
@@ -7715,7 +7721,7 @@
 (call it \tcode{A}) as described in~\ref{temp.deduct.type}.
 If the \grammarterm{conversion-function-id} is constructed during
 overload resolution\iref{over.match.funcs},
-the following transformations apply.
+the rules in the remainder of this subclause apply.
 
 \pnum
 If \tcode{P} is a reference type, the type referred to by \tcode{P} is used in place
@@ -7780,8 +7786,9 @@
 (i.e., the type referred to by the reference).
 \item
 If the original \tcode{A} is
-a function pointer or pointer-to-member-function type,
-its \keyword{noexcept}.
+a function pointer or pointer-to-member-function type
+with a potentially-throwing exception specification\iref{except.spec},
+the exception specification.
 \item
 Any cv-qualifiers in \tcode{A}
 that can be restored by a qualification conversion.

source/uax31.tex

@@ -85,14 +85,13 @@
 \rSec1[uaxid.pattern]{R3 Pattern_White_Space and Pattern_Syntax characters}
 
 \pnum
-UAX \#31 describes how languages that use or interpret patterns of characters,
-such as regular expressions or number formats,
-may describe that syntax with Unicode properties.
+UAX \#31 describes how formal languages
+such as computer languages should describe and implement
+their use of whitespace and syntactically significant characters
+during the processes of lexing and parsing.
 
 \pnum
-\Cpp{} does not do this as part of the language,
-deferring to library components for such usage of patterns.
-This requirement does not apply to \Cpp{}.
+\Cpp{} does not claim conformance with this requirement.
 
 \rSec1[uaxid.eqn]{R4 Equivalent normalized identifiers}