P3920R0 Wording for NB comment resolution on trivial relocation

Also fixes NB BDS 2-034, CA-133, CA-136, CA-137, CN 6.9.1p9,
FR 002-025, US 9-024, US 10-023, US 44-082, US 45-081, US 46-085,
US 47-084, and US 73-131 (C++26 CD).

Author: AlisdairM

source/basic.tex

@@ -5230,15 +5230,6 @@
 Scalar types, trivially copyable class types\iref{class.prop},
 arrays of such types, and cv-qualified versions of these
 types are collectively called \defnadjx{trivially copyable}{types}{type}.
-\label{term.trivially.relocatable.type}%
-Scalar types, trivially relocatable class types\iref{class.prop},
-arrays of such types, and cv-qualified versions of these
-types are collectively called \defnadjx{trivially relocatable}{types}{type}.
-\label{term.replaceable.type}%
-\indextext{replaceable!type|see{type, replaceable}}%
-Cv-unqualified scalar types, replaceable class types\iref{class.prop}, and
-arrays of such types are collectively called
-\defnx{replaceable types}{type!replaceable}.
 \label{term.standard.layout.type}%
 Scalar types, standard-layout class
 types\iref{class.prop}, arrays of such types, and

source/classes.tex

@@ -52,9 +52,7 @@
 
 \begin{bnf}
 \nontermdef{class-property-specifier}\br
-    \keyword{final}\br
-    \keyword{trivially_relocatable_if_eligible}\br
-    \keyword{replaceable_if_eligible}
+    \keyword{final}
 \end{bnf}
 
 \begin{bnf}
@@ -131,8 +129,7 @@
 within a single \grammarterm{class-property-specifier-seq}.
 Whenever a \grammarterm{class-key} is followed
 by a \grammarterm{class-head-name},
-one of the identifiers \tcode{final}, \tcode{trivially_relocatable_if_eligible},
-or \tcode{replaceable_if_eligible}, and a colon or left brace,
+the identifier \tcode{final}, and a colon or left brace,
 the identifier is interpreted as a \grammarterm{class-property-specifier}.
 \begin{example}
 \begin{codeblock}
@@ -142,10 +139,8 @@
 
 struct X {
  struct C { constexpr operator int() { return 5; } };
- struct B trivially_relocatable_if_eligible : C{};
-                        // OK, definition of nested class \tcode{B},
-                        // not declaration of a bit-field member
-                        // \tcode{trivially_relocatable_if_eligible}
+ struct B final : C{};  // OK, definition of nested class \tcode{B},
+                        // not declaration of a bit-field member \tcode{final}
 };
 \end{codeblock}
 \end{example}
@@ -187,88 +182,6 @@
 \item that has a trivial, non-deleted destructor\iref{class.dtor}.
 \end{itemize}
 
-\pnum
-A class \tcode{C} is \defn{default-movable} if
-
-\begin{itemize}
-\item overload resolution for direct-initializing an object of type \tcode{C}
-from an xvalue of type \tcode{C} selects a constructor that is a direct member
-of \tcode{C} and is neither user-provided nor deleted,
-
-\item overload resolution for assigning to an lvalue of type \tcode{C} from an
-xvalue of type \tcode{C} selects an assignment operator function that is a
-direct member of \tcode{C} and is neither user-provided nor deleted, and
-
-\item \tcode{C} has a destructor that is neither user-provided nor deleted.
-\end{itemize}
-
-\pnum
-A class is \defn{eligible for trivial relocation} unless it
-\begin{itemize}
-\item has any virtual base classes,
-\item has a base class that is not a trivially relocatable class,
-\item has a non-static data member of an object type that is not of a
-trivially relocatable type, or
-
-\item has a deleted destructor,
-\end{itemize}
-except that it is \impldef{whether an otherwise-eligible union having one or
-more subobjects of polymorphic class type is eligible for trivial relocation}
-whether an otherwise-eligible union having one or more subobjects of
-polymorphic class type is eligible for trivial relocation.
-
-\pnum
-A class \tcode{C} is a \defnadj{trivially relocatable}{class}
-if it is eligible for trivial relocation and
-\begin{itemize}
-\item has the \tcode{trivially_relocatable_if_eligible} \grammarterm{class-property-specifier},
-\item is a union with no user-declared special member functions, or
-\item is default-movable.
-\end{itemize}
-
-\pnum
-\begin{note}
-A class with const-qualified or reference non-static data members can be
-trivially relocatable.
-\end{note}
-
-\pnum
-A class \tcode{C} is \defn{eligible for replacement} unless
-\begin{itemize}
-\item it has a base class that is not a replaceable class,
-\item it has a non-static data member that is not of a replaceable type,
-\item overload resolution fails or selects a deleted constructor when
-direct-initializing an object of type \tcode{C} from an xvalue of type
-\tcode{C}\iref{dcl.init.general},
-
-\item overload resolution fails or selects a deleted assignment operator
-function when assigning to an lvalue of type \tcode{C} from an xvalue of type
-\tcode{C}\iref{expr.assign,over.assign}, or
-
-\item it has a deleted destructor.
-\end{itemize}
-
-\indextext{replaceable!class|see{class, replaceable}}%
-\pnum
-A class \tcode{C} is a \defnx{replaceable class}{class!replaceable} if it is
-eligible for replacement and
-\begin{itemize}
-\item has the \tcode{replaceable_if_eligible} \grammarterm{class-property-specifier},
-\item is a union with no user-declared special member functions, or
-\item is default-movable.
-\end{itemize}
-
-\pnum
-\begin{note}
-Accessibility of the special member functions is not considered when
-establishing trivial relocatability or replaceability.
-\end{note}
-
-\pnum
-\begin{note}
-Not all trivially copyable classes are trivially relocatable or replaceable.
-\end{note}
-
 \pnum
 A class \tcode{S} is a \defnadj{standard-layout}{class} if it:
 \begin{itemize}

source/compatibility.tex

@@ -107,22 +107,6 @@
 
 \rSec2[diff.cpp23.dcl.dcl]{\ref{dcl}: declarations}
 
-\diffref{dcl.decl.general}
-\change
-Introduction of \tcode{trivially_relocatable_if_eligible} and
-\tcode{replaceable_if_eligible} as identifiers with special meaning\iref{lex.name}.
-\rationale
-Support declaration of trivially relocatable and replaceable types\iref{class.prop}.
-\effect
-Valid \CppXXIII{} code can become ill-formed.
-\begin{example}
-\begin{codeblock}
-struct C {};
-struct C replaceable_if_eligible {};    // was well-formed (new variable \tcode{replaceable_if_eligible})
-                                        // now ill-formed (redefines \tcode{C})
-\end{codeblock}
-\end{example}
-
 \diffref{dcl.init.list}
 \change
 Pointer comparisons between \tcode{initializer_list} objects' backing arrays
@@ -262,17 +246,6 @@
 Valid \CppXXIII{} code that \tcode{\#include}{s} headers with these names may be
 invalid in this revision of \Cpp{}.
 
-\diffref{res.on.macro.definitions}
-\change
-Additional restrictions on macro names.
-\rationale
-Avoid hard to diagnose or non-portable constructs.
-\effect
-Names of special identifiers may not be used as macro names.
-Valid \CppXXIII{} code that defines \tcode{replaceable_if_eligible} or
-\tcode{trivially_relocatable_if_eligible} as macros is invalid
-in this revision of \Cpp{}.
-
 \rSec2[diff.cpp23.mem]{\ref{mem}: memory management library}
 
 \diffref{c.malloc}

source/expressions.tex

@@ -2231,9 +2231,7 @@
 other than by changing:
 \begin{itemize}
 \item the size and/or alignment of the closure type,
-\item whether the closure type is trivially copyable\iref{class.prop},
-\item whether the closure type is trivially relocatable\iref{class.prop},
-\item whether the closure type is replaceable\iref{class.prop}, or
+\item whether the closure type is trivially copyable\iref{class.prop}, or
 \item whether the closure type is a standard-layout class\iref{class.prop}.
 \end{itemize}
 

source/lex.tex

@@ -966,8 +966,6 @@
 \indextext{\idxcode{final}}%
 \indextext{\idxcode{module}}%
 \indextext{\idxcode{override}}%
-\indextext{\idxcode{replaceable_if_eligible}}%
-\indextext{\idxcode{trivially_relocatable_if_eligible}}%
 The identifiers in \tref{lex.name.special} have a special meaning when
 appearing in a certain context. When referred to in the grammar, these identifiers
 are used explicitly rather than using the \grammarterm{identifier} grammar production.
@@ -976,15 +974,18 @@
 token as a regular \grammarterm{identifier}.
 
 \begin{multicolfloattable}{Identifiers with special meaning}{lex.name.special}
-{llll}
-\keyword{final}                                 \\
-\keyword{override}                              \\\columnbreak
-\keyword{import}                                \\
-\keyword{module}                                \\\columnbreak
-\keyword{post}                                  \\
-\keyword{pre}                                   \\\columnbreak
-\keyword{replaceable_if_eligible}               \\
-\keyword{trivially_relocatable_if_eligible}     \\
+{llllll}
+\keyword{final}           \\
+\columnbreak
+\keyword{import}          \\
+\columnbreak
+\keyword{module}          \\
+\columnbreak
+\keyword{override}        \\
+\columnbreak
+\keyword{post}            \\
+\columnbreak
+\keyword{pre}             \\
 \end{multicolfloattable}
 
 \pnum

source/lib-intro.tex

@@ -3850,20 +3850,6 @@
 \ref{depr} is a trivially copyable class, a standard-layout class, or an
 implicit-lifetime class\iref{class.prop}.
 
-\pnum
-Unless explicitly stated otherwise, it is unspecified whether any class for
-which trivial relocation (i.e., the effects of
-\tcode{trivially_relocate}\iref{obj.lifetime}) would be semantically equivalent
-to move-construction of the destination object followed by destruction of the
-source object is a trivially relocatable class\iref{class.prop}.
-
-\pnum
-Unless explicitly stated otherwise, it is unspecified whether a class \tcode{C}
-is a replaceable class\iref{class.prop} if assigning an xvalue \tcode{a} of
-type \tcode{C} to an object \tcode{b} of type \tcode{C} is semantically
-equivalent to destroying \tcode{b} and then constructing from \tcode{a} in
-\tcode{b}'s place.
-
 \rSec3[protection.within.classes]{Protection within classes}
 
 \pnum

source/memory.tex

@@ -105,10 +105,6 @@
   template<class T>
     const volatile T* start_lifetime_as_array(const volatile void* p,               // freestanding
 	                                      size_t n) noexcept;
-  template<class T>
-    T* trivially_relocate(T* first, T* last, T* result);                            // freestanding
-  template<class T>
-    constexpr T* relocate(T* first, T* last, T* result);                            // freestanding
 
   // \ref{allocator.tag}, allocator argument tag
   struct allocator_arg_t { explicit allocator_arg_t() = default; };                 // freestanding
@@ -1135,128 +1131,6 @@
 a pointer that compares equal to \tcode{p}\iref{expr.eq}.
 \end{itemdescr}
 
-\indexlibraryglobal{trivially_relocate}%
-\begin{itemdecl}
-template<class T>
-  T* trivially_relocate(T* first, T* last, T* result);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\mandates
-\tcode{is_trivially_relocatable_v<T> \&\& !is_const_v<T>} is \tcode{true}.
-\tcode{T} is not an array of unknown bound.
-
-\pnum
-\expects
-\begin{itemize}
-\item
-  \range{first}{last} is a valid range.
-\item
-  \range{result}{result + (last - first)} denotes a region of storage that
-  is a subset of the region reachable through \tcode{result}\iref{basic.compound}
-  and suitably aligned for the type \tcode{T}.
-\item
-  No element in the range \range{first}{last} is a potentially-overlapping subobject.
-\end{itemize}
-
-\pnum
-\ensures
-No effect if \tcode{result == first} is \tcode{true}.
-Otherwise, the range denoted by \range{result}{result + (last - first)}
-contains objects (including subobjects) whose lifetime has begun and whose
-object representations are the original object representations of the
-corresponding objects in the source range \range{first}{last} except
-for any parts of the object representations used by the implementation to
-represent type information\iref{intro.object}. If any of the objects has
-union type, its active member is the same as that of the corresponding object
-in the source range. If any of the aforementioned objects has a non-static
-data member of reference type, that reference refers to the same entity as
-does the corresponding reference in the source range. The lifetimes of the
-original objects in the source range have ended.
-
-\pnum
-\returns
-\tcode{result + (last - first)}.
-
-\pnum
-\throws
-Nothing.
-
-\pnum
-\complexity
-Linear in the length of the source range.
-
-\pnum
-\remarks
-The destination region of storage is considered reused\iref{basic.life}.
-No constructors or destructors are invoked.
-
-\begin{note}
-Overlapping ranges are supported.
-\end{note}
-\end{itemdescr}
-
-\indexlibraryglobal{relocate}%
-\begin{itemdecl}
-template<class T>
-  constexpr T* relocate(T* first, T* last, T* result);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\mandates
-\tcode{is_nothrow_relocatable_v<T> \&\& !is_const_v<T>} is \tcode{true}.
-\tcode{T} is not an array of unknown bound.
-
-\pnum
-\expects
-\begin{itemize}
-\item
-  \range{first}{last} is a valid range.
-\item
-  \range{result}{result + (last - first)} denotes a region of storage that is
-  a subset of the region reachable through \tcode{result}\iref{basic.compound}
-  and suitably aligned for the type \tcode{T}.
-\item
-  No element in the range \range{first}{last} is a potentially-overlapping
-  subobject.
-\end{itemize}
-
-\pnum
-\effects
-\begin{itemize}
-\item
-  If \tcode{result == first} is \tcode{true}, no effect;
-\item
-  otherwise, if not called during constant evaluation and
-  \tcode{is_trivially_relocatable_v<T>} is \tcode{true}, then has
-  effects equivalent to: \tcode{trivially_relocate(first, last, result);}
-\item
-  otherwise, for each integer \tcode{i} in  \range{0}{last - first},
-  \begin{itemize}
-  \item
-    if \tcode{T} is an array type, equivalent to:
-    \tcode{relocate(begin(first[i]), end(first[i]), *start_lifetime_as<T>(result + i));}
-  \item
-    otherwise, equivalent to:
-    \tcode{construct_at(result + i, std::move(first[i])); destroy_at(first + i);}
-  \end{itemize}
-\end{itemize}
-
-\pnum
-\returns
-\tcode{result + (last - first)}.
-
-\pnum
-\throws
-Nothing.
-
-\begin{note}
-Overlapping ranges are supported.
-\end{note}
-\end{itemdescr}
-
 \rSec2[allocator.tag]{Allocator argument tag}
 
 \indexlibraryglobal{allocator_arg_t}%