P1874R1 Dynamic Initialization Order of Non-Local Variables in Modules

Fixes NB US 082 (C++20 CD)

Author: jensmaurer

source/basic.tex

@@ -6374,31 +6374,42 @@
 variable template specialization has ordered initialization.
 \end{note}
 
+\pnum
+A declaration \tcode{D} is
+\defn{appearance-ordered} before a declaration \tcode{E} if
+\begin{itemize}
+\item \tcode{D} appears in the same translation unit as \tcode{E}, or
+\item the translation unit containing \tcode{E}
+has an interface dependency on the translation unit containing \tcode{D},
+\end{itemize}
+in either case prior to \tcode{E}.
+
 \pnum
 Dynamic initialization of non-local variables \tcode{V} and \tcode{W}
 with static storage duration are ordered as follows:
 \begin{itemize}
 \item
-If \tcode{V} and \tcode{W} have
-ordered initialization and \tcode{V} is defined before \tcode{W} within
-a single translation unit, the initialization of \tcode{V} is sequenced
-before the initialization of \tcode{W}.
-
-\item
-If \tcode{V} has partially-ordered initialization, \tcode{W} does not have
-unordered initialization, and \tcode{V} is defined before \tcode{W} in
-every translation unit in which \tcode{W} is defined, then
+If \tcode{V} and \tcode{W} have ordered initialization and
+the definition of \tcode{V}
+is appearance-ordered before the definition of \tcode{W}, or
+if \tcode{V} has partially-ordered initialization,
+\tcode{W} does not have unordered initialization, and
+for every definition \tcode{E} of \tcode{W}
+there exists a definition \tcode{D} of \tcode{V}
+such that \tcode{D} is appearance-ordered before \tcode{E}, then
 \begin{itemize}
 \item
-if the program starts a thread\iref{intro.multithread}
-other than the main thread\iref{basic.start.main},
+if the program does not start a thread\iref{intro.multithread}
+other than the main thread\iref{basic.start.main}
+or \tcode{V} and \tcode{W} have ordered initialization and
+they are defined in the same translation unit,
 the initialization of \tcode{V}
-strongly happens before
+is sequenced before
 the initialization of \tcode{W};
 \item
 otherwise,
 the initialization of \tcode{V}
-is sequenced before
+strongly happens before
 the initialization of \tcode{W}.
 \end{itemize}