P3247R2 Deprecate the notion of trivial types

Author: jensmaurer

source/basic.tex

@@ -4959,11 +4959,6 @@
 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.trivial.type}%
-Scalar types, trivial class types\iref{class.prop},
-arrays of such types, and cv-qualified versions of these
-types are collectively called
-\defnadjx{trivial}{types}{type}.
 \label{term.standard.layout.type}%
 Scalar types, standard-layout class
 types\iref{class.prop}, arrays of such types, and

source/classes.tex

@@ -172,15 +172,6 @@
 \item that has a trivial, non-deleted destructor\iref{class.dtor}.
 \end{itemize}
 
-\pnum
-A \defnadj{trivial}{class} is a class that is trivially copyable and
-has one or more eligible default constructors\iref{class.default.ctor},
-all of which are trivial.
-\begin{note}
-In particular, a trivially copyable or trivial class does not have
-virtual functions or virtual base classes.
-\end{note}
-
 \pnum
 A class \tcode{S} is a \defnadj{standard-layout}{class} if it:
 \begin{itemize}
@@ -272,25 +263,25 @@
 \pnum
 \begin{example}
 \begin{codeblock}
-struct N {          // neither trivial nor standard-layout
+struct N {          // neither trivially copyable nor standard-layout
   int i;
   int j;
   virtual ~N();
 };
 
-struct T {          // trivial but not standard-layout
+struct T {          // trivially copyable but not standard-layout
   int i;
 private:
   int j;
 };
 
-struct SL {         // standard-layout but not trivial
+struct SL {         // standard-layout but not trivially copyable
   int i;
   int j;
   ~SL();
 };
 
-struct POD {        // both trivial and standard-layout
+struct POD {        // both trivially copyable and standard-layout
   int i;
   int j;
 };
@@ -5941,7 +5932,7 @@
 B bobj;                                 // definition of \tcode{bobj}
 
 extern X xobj;
-int* p3 = &xobj.i;                      // OK, \tcode{X} is a trivial class
+int* p3 = &xobj.i;                      // OK, all constructors of \tcode{X} are trivial
 X xobj;
 \end{codeblock}
 For another example,

source/containers.tex

@@ -9536,8 +9536,9 @@
 
 \pnum
 For any $\tcode{N} > 0$,
-if \tcode{is_trivial_v<T>} is \tcode{false}, then
-no \tcode{inplace_vector<T, N>} member functions
+if \tcode{T} is not trivially copyable or
+\tcode{is_trivially_default_constructible_v<T>} is \tcode{false},
+then no \tcode{inplace_vector<T, N>} member functions
 are usable in constant expressions.
 
 \pnum
@@ -20617,13 +20618,13 @@
 \end{codeblock}
 
 \pnum
-Each of \tcode{layout_left}, \tcode{layout_right}, and \tcode{layout_stride}
-meets the layout mapping policy requirements and is a trivial type.
-
-\pnum
-Each specialization of
-\tcode{layout_left_padded} and \tcode{layout_right_padded}
-meets the layout mapping policy requirements and is a trivial type.
+Each of \tcode{layout_left}, \tcode{layout_right}, and \tcode{layout_stride},
+as well as each specialization of
+\tcode{layout_left_padded} and \tcode{layout_right_padded},
+meets the layout mapping policy requirements and is a trivially copyable type.
+Furthermore,
+\tcode{is_trivially_default_constructible_v<T>} is \tcode{true}
+for any such type \tcode{T}.
 
 \rSec4[mdspan.layout.left]{Class template \tcode{layout_left::mapping}}
 

source/future.tex

@@ -286,6 +286,8 @@
 
 \begin{codeblock}
 namespace std {
+  template<class T> struct is_trivial;
+  template<class T> constexpr bool is_trivial_v = is_trivial<T>::value;
   template<class T> struct is_pod;
   template<class T> constexpr bool is_pod_v = is_pod<T>::value;
   template<size_t Len, size_t Align = @\exposid{default-alignment}@> // \seebelow
@@ -304,13 +306,48 @@
 any of the templates defined in this subclause is undefined,
 unless explicitly permitted by the specification of the corresponding template.
 
+\pnum
+\label{term.trivial.type}%
+A \defnadj{trivial}{class} is a class that is trivially copyable and
+has one or more eligible default constructors, all of which are trivial.
+\begin{note}
+In particular,
+a trivial class does not have virtual functions or virtual base classes.
+\end{note}
+A \defnadj{trivial}{type} is a scalar type, a trivial class,
+an array of such a type, or a cv-qualified version of one of these types..
+
 \pnum
 \indextext{POD}%
 A \term{POD class} is a class that is both a trivial class and a
 standard-layout class, and has no non-static data members of type non-POD class
 (or array thereof). A \term{POD type} is a scalar type, a POD class, an array
 of such a type, or a cv-qualified version of one of these types.
 
+\indexlibraryglobal{is_trivial}%
+\begin{itemdecl}
+template<class T> struct is_trivial;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\expects
+\tcode{remove_all_extents_t<T>} shall be a complete type or \cv{} \keyword{void}.
+
+\pnum
+\remarks
+\tcode{is_trivial<T>} is a \oldconcept{UnaryTypeTrait}\iref{meta.rqmts}
+with a base characteristic of \tcode{true_type}
+if \tcode{T} is a trivial type,
+and \tcode{false_type} otherwise.
+
+\pnum
+\begin{note}
+It is unspecified
+whether a closure type\iref{expr.prim.lambda.closure} is a trivial type.
+\end{note}
+\end{itemdescr}
+
 \indexlibraryglobal{is_pod}%
 \begin{itemdecl}
 template<class T> struct is_pod;

source/meta.tex

@@ -192,7 +192,6 @@
   // \ref{meta.unary.prop}, type properties
   template<class T> struct is_const;
   template<class T> struct is_volatile;
-  template<class T> struct is_trivial;
   template<class T> struct is_trivially_copyable;
   template<class T> struct is_standard_layout;
   template<class T> struct is_empty;
@@ -430,8 +429,6 @@
     constexpr bool @\libglobal{is_const_v}@ = is_const<T>::value;
   template<class T>
     constexpr bool @\libglobal{is_volatile_v}@ = is_volatile<T>::value;
-  template<class T>
-    constexpr bool @\libglobal{is_trivial_v}@ = is_trivial<T>::value;
   template<class T>
     constexpr bool @\libglobal{is_trivially_copyable_v}@ = is_trivially_copyable<T>::value;
   template<class T>
@@ -832,13 +829,6 @@
  \tcode{T} is volatile-qualified\iref{basic.type.qualifier}                   &   \\ \rowsep
 
 
-\indexlibraryglobal{is_trivial}%
-\tcode{template<class T>}\br
- \tcode{struct is_trivial;}                 &
- \tcode{T} is a trivial type\iref{term.trivial.type}     &
- \tcode{remove_all_extents_t<T>} shall be a complete
- type or \cv{}~\keyword{void}.                \\ \rowsep
-
 \indexlibraryglobal{is_trivially_copyable}%
 \tcode{template<class T>}\br
  \tcode{struct is_trivially_copyable;}      &

source/strings.tex

@@ -5,7 +5,8 @@
 
 \pnum
 This Clause describes components for manipulating sequences of
-any non-array trivial standard-layout\iref{term.standard.layout.type} type.
+any non-array trivially copyable standard-layout\iref{term.standard.layout.type} type \tcode{T}
+where \tcode{is_trivially_default_constructible_v<T>} is \tcode{true}.
 Such types are called \defnx{char-like types}{char-like type},
 and objects of
 char-like types are called \defnx{char-like objects}{char-like object} or

source/support.tex

@@ -333,9 +333,10 @@
 \pnum
 The type
 \indexlibraryglobal{max_align_t}%
-\tcode{max_align_t} is a trivial standard-layout type whose alignment requirement
+\tcode{max_align_t} is a trivially copyable standard-layout type whose alignment requirement
 is at least as great as that of every scalar type, and whose alignment
 requirement is supported in every context\iref{basic.align}.
+\tcode{std::is_trivially_default_constructible_v<max_align_t>} is \tcode{true}.
 
 \xrefc{7.19}