LWG4026 Assignment operators of std::expected should propagate triviality

burblebee · tkoeppe · commit 13b42a20d6ed · 2026-04-14T12:20:05.000+01:00
Fixes NB US 135-216, US 136-217 (C++26 CD).
diff --git a/source/utilities.tex b/source/utilities.tex
@@ -8736,6 +8736,17 @@
 \tcode{is_nothrow_move_constructible_v<T> || is_nothrow_move_constructible_v<E>}
 is \tcode{true}.
 \end{itemize}
+
+\pnum
+This operator is trivial if:
+\begin{itemize}
+\item \tcode{is_trivially_copy_constructible_v<T>} is \tcode{true}, and
+\item \tcode{is_trivially_copy_assignable_v<T>} is \tcode{true}, and
+\item \tcode{is_trivially_destructible_v<T>} is \tcode{true}, and
+\item \tcode{is_trivially_copy_constructible_v<E>} is \tcode{true}, and
+\item \tcode{is_trivially_copy_assignable_v<E>} is \tcode{true}, and
+\item \tcode{is_trivially_destructible_v<E>} is \tcode{true}.
+\end{itemize}
 \end{itemdescr}
 
 \indexlibrarymember{operator=}{expected}%
@@ -8793,6 +8804,17 @@
 is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T> &&
 is_nothrow_move_assignable_v<E> && is_nothrow_move_constructible_v<E>
 \end{codeblock}
+
+\pnum
+This operator is trivial if:
+\begin{itemize}
+\item \tcode{is_trivially_move_constructible_v<T>} is \tcode{true}, and
+\item \tcode{is_trivially_move_assignable_v<T>} is \tcode{true}, and
+\item \tcode{is_trivially_destructible_v<T>} is \tcode{true}, and
+\item \tcode{is_trivially_move_constructible_v<E>} is \tcode{true}, and
+\item \tcode{is_trivially_move_assignable_v<E>} is \tcode{true}, and
+\item \tcode{is_trivially_destructible_v<E>} is \tcode{true}.
+\end{itemize}
 \end{itemdescr}
 
 \indexlibrarymember{operator=}{expected}%
@@ -9940,6 +9962,13 @@
 This operator is defined as deleted unless
 \tcode{is_copy_assignable_v<E>} is \tcode{true} and
 \tcode{is_copy_constructible_v<E>} is \tcode{true}.
+
+\pnum
+This operator is trivial if
+\tcode{is_trivially_copy_constructible_v<E>},
+\tcode{is_trivially_copy_assigna\-ble_v<E>}, and
+\tcode{is_trivially_destructible_v<E>}
+are all \tcode{true}.
 \end{itemdescr}
 
 \indexlibrarymember{operator=}{expected<void>}%
@@ -9979,6 +10008,13 @@
 \remarks
 The exception specification is equivalent to
 \tcode{is_nothrow_move_constructible_v<E> \&\& is_nothrow_move_assignable_v<E>}.
+
+\pnum
+This operator is trivial if
+\tcode{is_trivially_move_constructible_v<E>},
+\tcode{is_trivially_move_assigna\-ble_v<E>}, and
+\tcode{is_trivially_destructible_v<E>}
+are all \tcode{true}.
 \end{itemdescr}
 
 \indexlibrarymember{operator=}{expected<void>}%
