LWG4304 std::optional<NonReturnable&> is ill-formed due to value_or

Author: burblebee

source/utilities.tex

@@ -4886,6 +4886,10 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is a non-array object type.
+
 \pnum
  Let \tcode{X} be \tcode{remove_cv_t<T>}.
 
@@ -4899,6 +4903,14 @@
 \begin{codeblock}
 return has_value() ? *@\exposid{val}@ : static_cast<X>(std::forward<U>(u));
 \end{codeblock}
+
+\pnum
+\remarks
+The return type is unspecified if
+\tcode{T} is an array type or a non-object type.
+\begin{note}
+This is to avoid the declaration being ill-formed.
+\end{note}
 \end{itemdescr}
 
 \rSec3[optional.ref.monadic]{Monadic operations}