Merge 2022-11 CWG Motion 1

P2709R0 Core Language Working Group "ready" issues for the November, 2022 meeting; excluding issues 2635 and 2602

Author: tkoeppe

source/basic.tex

@@ -882,6 +882,7 @@
 \item
 their object parameters have the same type.
 \end{itemize}
+\indextext{template!function!corresponding object parameter}%
 Two non-static member function templates have
 \defnadjx{corresponding}{object parameters}{object parameter} if:
 \begin{itemize}
@@ -894,6 +895,14 @@
 \item
 the types of their object parameters are equivalent.
 \end{itemize}
+\indextext{template!function!corresponding signature}%
+Two function templates have
+\defnadjx{corresponding}{signatures}{signature} if
+their \grammarterm{template-parameter-list}{s}
+have the same length,
+their corresponding \grammarterm{template-parameter}{s} are equivalent,
+they have equivalent non-object-parameter-type-lists and return types (if any), and,
+if both are non-static members, they have corresponding object parameters.
 
 \pnum
 Two declarations \defn{correspond}
@@ -925,13 +934,9 @@
 if both are non-static members,
 they have corresponding object parameters, or
 \item
-both declare function templates with equivalent
-non-object-parameter-type-lists,
-return types (if any),
-\grammarterm{template-head}s, and
-trailing \grammarterm{requires-clause}s (if any), and,
-if both are non-static members,
-they have corresponding object parameters.
+both declare function templates with corresponding signatures and equivalent
+\grammarterm{template-head}s and
+trailing \grammarterm{requires-clause}s (if any).
 \end{itemize}
 \end{itemize}
 \begin{note}
@@ -3426,8 +3431,7 @@
 program has undefined behavior if:
 \begin{itemize}
 \item
-  the object will be or was of a class type with a non-trivial destructor
-  and the pointer is used as the operand of a \grammarterm{delete-expression},
+  the pointer is used as the operand of a \grammarterm{delete-expression},
 \item
   the pointer is used to access a non-static data member or call a
   non-static member function of the object, or
@@ -4742,15 +4746,20 @@
 has all of the following properties:
 \begin{itemize}
 \item it has a constexpr destructor\iref{dcl.constexpr},
-\item it is either a closure type\iref{expr.prim.lambda.closure},
-an aggregate type\iref{dcl.init.aggr}, or
-has at least one constexpr constructor or constructor template
+\item all of its non-static non-variant data members and base classes are of non-volatile literal types, and
+\item it
+\begin{itemize}
+\item is a closure type\iref{expr.prim.lambda.closure},
+\item is an aggregate union type that has either
+no variant members or
+at least one variant member of non-volatile literal type,
+\item is a non-union aggregate type for which
+each of its anonymous union members
+satisfies the above requirements for an aggregate union type, or
+\item has at least one constexpr constructor or constructor template
 (possibly inherited\iref{namespace.udecl} from a base class)
-that is not a copy or move constructor,
-\item if it is a union, at least one of its non-static data members is
-of non-volatile literal type, and
-\item if it is not a union, all of its non-static data members and base classes are
-of non-volatile literal types.
+that is not a copy or move constructor.
+\end{itemize}
 \end{itemize}
 \end{itemize}
 \begin{note}

source/classes.tex

@@ -305,7 +305,7 @@
 A class \tcode{S} is an \defnadj{implicit-lifetime}{class} if
 \begin{itemize}
 \item
-it is an aggregate or
+it is an aggregate whose destructor is not user-provided or
 \item
 it has at least one trivial eligible constructor and
 a trivial, non-deleted destructor.
@@ -605,10 +605,9 @@
 \end{note}
 
 \pnum
-A class is considered a completely-defined object
-type\iref{term.incomplete.type} (or complete type) at the closing \tcode{\}} of
-the \grammarterm{class-specifier}.
-The class is regarded as complete within its complete-class contexts;
+A class is regarded as complete
+where its definition is reachable and
+within its complete-class contexts;
 otherwise it is regarded as incomplete within its own class
 \grammarterm{member-specification}.
 
@@ -785,13 +784,21 @@
 The \defn{common initial sequence} of two standard-layout struct\iref{class.prop}
 types is the longest sequence of non-static data
 members and bit-fields in declaration order, starting with the first
-such entity in each of the structs, such that corresponding entities
+such entity in each of the structs, such that
+\begin{itemize}
+\item
+corresponding entities
 have layout-compatible types\iref{basic.types},
+\item
+corresponding entities have the same alignment requirements\iref{basic.align},
+\item
 either both entities are declared with
 the \tcode{no_unique_address} attribute\iref{dcl.attr.nouniqueaddr}
-or neither is,
-and either both entities are bit-fields with the same width
+or neither is, and
+\item
+either both entities are bit-fields with the same width
 or neither is a bit-field.
+\end{itemize}
 \begin{example}
 \begin{codeblock}
 struct A { int a; char b; };

source/compatibility.tex

@@ -657,6 +657,31 @@
 }
 \end{codeblock}
 
+\diffref{over.match.oper}
+\change
+Overload resolution may change for equality operators\iref{expr.eq}.
+\rationale
+Support calling \tcode{operator==} with reversed order of arguments.
+\effect
+Valid \CppXVII{} code that uses equality operators with conversion functions
+may be ill-formed or have different semantics in this revision of \Cpp{}.
+For example:
+\begin{codeblock}
+struct A {
+  operator int() const { return 10; }
+};
+
+bool operator==(A, int);        // \#1
+// \#2 is built-in candidate: \tcode{bool operator==(int, int);}
+bool b = 10 == A();             // calls \#1 with reversed order of arguments; previously selected \#2
+
+struct B {
+  bool operator==(const B&);    // member function with no cv-qualifier
+};
+B b1;
+bool eq = (b1 == b1);           // ambiguous; previously well-formed
+\end{codeblock}
+
 \rSec2[diff.cpp17.temp]{\ref{temp}: templates}
 
 \diffref{temp.names}

source/declarations.tex

@@ -2323,12 +2323,16 @@
 \pnum
 The ambiguity arising from the similarity between a function-style cast and
 a declaration mentioned in~\ref{stmt.ambig} can also occur in the context of a declaration.
-In that context, the choice is between a function declaration with
-a redundant set of parentheses around a parameter name and an object declaration
-with a function-style cast as the initializer.
+In that context, the choice is between
+an object declaration
+with a function-style cast as the initializer and
+a declaration involving a function declarator
+with a redundant set of parentheses around a parameter name.
 Just as for the ambiguities mentioned in~\ref{stmt.ambig},
-the resolution is to consider any construct that could possibly
-be a declaration a declaration.
+the resolution is to consider any construct,
+such as the potential parameter declaration,
+that could possibly be a declaration
+to be a declaration.
 \begin{note}
 A declaration can be explicitly disambiguated by adding parentheses
 around the argument.
@@ -4455,7 +4459,8 @@
 as well as in argument passing, function return,
 throwing an exception\iref{except.throw},
 handling an exception\iref{except.handle},
-and aggregate member initialization\iref{dcl.init.aggr},
+and aggregate member initialization other than by a
+\grammarterm{designated-initializer-clause}\iref{dcl.init.aggr},
 is called
 \defn{copy-initialization}.
 \begin{note}
@@ -4548,7 +4553,7 @@
 is the same class as the class of the destination,
 the initializer expression is used to initialize the destination object.
 \begin{example}
-\tcode{T x = T(T(T()));} calls the \tcode{T} default constructor to initialize \tcode{x}.
+\tcode{T x = T(T(T()));} value-initializes \tcode{x}.
 \end{example}
 \item
 Otherwise, if the initialization is direct-initialization,
@@ -4680,6 +4685,14 @@
 An \grammarterm{initializer-clause} followed by an ellipsis is a
 pack expansion\iref{temp.variadic}.
 
+\pnum
+Initialization includes
+the evaluation of all subexpressions of
+each \grammarterm{initializer-clause} of
+the initializer (possibly nested within \grammarterm{braced-init-list}{s}) and
+the creation of any temporary objects for
+function arguments or return values\iref{class.temporary}.
+
 \pnum
 If the initializer is a parenthesized \grammarterm{expression-list},
 the expressions are evaluated in the order
@@ -4736,9 +4749,9 @@
 \item
 no private or protected direct non-static data members\iref{class.access},
 \item
-no virtual functions\iref{class.virtual}, and
+no private or protected direct base classes\iref{class.access.base}, and
 \item
-no virtual, private, or protected base classes\iref{class.mi}.
+no virtual functions\iref{class.virtual} or virtual base classes\iref{class.mi}.
 \end{itemize}
 \begin{note}
 Aggregate initialization does not allow accessing
@@ -4790,7 +4803,7 @@
 the initializer list is
 a brace-enclosed \grammarterm{designated-initializer-list},
 the element is initialized by the
-\grammarterm{designated-initializer-list} \tcode{\{ }\placeholder{D}\tcode{ \}},
+\grammarterm{braced-init-list} \tcode{\{ }\placeholder{D}\tcode{ \}},
 where \placeholder{D} is the \grammarterm{designated-initializer-clause}
 naming a member of the anonymous union member.
 There shall be only one such \grammarterm{designated-initializer-clause}.
@@ -4818,6 +4831,11 @@
 a narrowing conversion\iref{dcl.init.list} is required
 to convert the expression, the program is ill-formed.
 \begin{note}
+If the initialization is by \grammarterm{designated-initializer-clause},
+its form determines whether copy-initialization or direct-initialization
+is performed.
+\end{note}
+\begin{note}
 If an initializer is itself an initializer list,
 the element is list-initialized, which will result in a recursive application
 of the rules in this subclause if the element is an aggregate.
@@ -5975,8 +5993,18 @@
 original type, or
 
 \item from an integer type or unscoped enumeration type to an integer type that cannot
-represent all the values of the original type, except where the source is a constant
+represent all the values of the original type, except where
+\begin{itemize}
+\item
+the source is a bit-field whose width $w$ is less than that of its type
+(or, for an enumeration type, its underlying type) and
+the target type can represent all the values
+of a hypothetical extended integer type
+with width $w$ and with the same signedness as the original type or
+\item
+the source is a constant
 expression whose value after integral promotions will fit into the target type, or
+\end{itemize}
 
 \item from a pointer type or a pointer-to-member type to \tcode{bool}.
 \end{itemize}
@@ -6448,19 +6476,20 @@
 where
 \begin{itemize}
 \item
+\indextext{coroutine!await expression}%
 the \grammarterm{await-expression} containing
 the call to \tcode{initial_suspend}
-is the \defn{initial suspend point}, and
+is the \defnadj{initial}{await expression}, and
 \item
 the \grammarterm{await-expression} containing
 the call to \tcode{final_suspend}
-is the \defn{final suspend point}, and
+is the \defnadj{final}{await expression}, and
 \item
 \placeholder{initial-await-resume-called}
 is initially \tcode{false} and is set to \tcode{true}
 immediately before the evaluation
 of the \placeholder{await-resume} expression\iref{expr.await}
-of the initial suspend point, and
+of the initial await expression, and
 \item
 \placeholder{promise-type} denotes the promise type, and
 \item
@@ -6476,7 +6505,19 @@
 constructor is found\iref{over.match.viable}, then
 \placeholder{promise-constructor-arguments} is
 \tcode{($\tcode{q}_1$, $\dotsc$, $\tcode{q}_n$)}, otherwise
-\placeholder{promise-constructor-arguments} is empty.
+\placeholder{promise-constructor-arguments} is empty, and
+\item
+a coroutine is suspended at the \defnadj{initial}{suspend point} if
+it is suspended at the initial await expression, and
+\item
+a coroutine is suspended at a \defnadj{final}{suspend point} if
+it is suspended
+\begin{itemize}
+\item
+at a final await expression or
+\item
+due to an exception exiting from \tcode{unhandled_exception()}.
+\end{itemize}
 \end{itemize}
 
 \pnum
@@ -6504,7 +6545,7 @@
 a resumption member function\iref{coroutine.handle.resumption}
 of a coroutine handle\iref{coroutine.handle}
 that refers to the coroutine.
-The function that invoked a resumption member function is
+The evaluation that invoked a resumption member function is
 called the \defnx{resumer}{coroutine!resumer}.
 Invoking a resumption member function for a coroutine
 that is not suspended results in undefined behavior.
@@ -6642,7 +6683,8 @@
 \pnum
 If the evaluation of the expression
 \tcode{\exposid{promise}.unhandled_exception()} exits via an exception,
-the coroutine is considered suspended at the final suspend point.
+the coroutine is considered suspended at the final suspend point
+and the exception propagates to the caller or resumer.
 
 \pnum
 The expression \keyword{co_await} \tcode{\exposid{promise}.final_suspend()}
@@ -7027,6 +7069,15 @@
 this range.
 \end{footnote}
 
+\pnum
+An enumeration has
+the same size,
+value representation, and
+alignment requirements\iref{basic.align}
+as its underlying type.
+Furthermore, each value of an enumeration has the same representation
+as the corresponding value of the underlying type.
+
 \pnum
 Two enumeration types are \defnx{layout-compatible enumerations}{layout-compatible!enumeration}
 if they have the same underlying type.
@@ -8691,7 +8742,8 @@
 a function,
 a namespace,
 an enumeration,
-an enumerator, or
+an enumerator,
+a concept, or
 a template specialization.
 
 \pnum