[diff.dcl] Discuss 'alignas' placement restrictions

jensmaurer · tkoeppe · commit 193cfc17cbb7 · 2022-08-18T18:24:19.000+01:00
diff --git a/source/compatibility.tex b/source/compatibility.tex
@@ -2719,6 +2719,27 @@
 Taking the size of an enumerator is not a
 common C coding practice.
 
+\diffref{dcl.align}
+\change
+In \Cpp{},
+an \grammarterm{alignment-specifier} is an \grammarterm{attribute-specifier}.
+In C, an \grammarterm{alignment-specifier} is a \gterm{declaration-specifier}.
+
+Example:
+\begin{codeblock}
+#include <stdalign.h>
+unsigned alignas(8) int x;      // valid C, invalid \Cpp{}
+unsigned int y alignas(8);      // valid \Cpp{}, invalid C
+\end{codeblock}
+\rationale
+\Cpp{} requires unambiguous placement of the \grammarterm{alignment-specifier}.
+\effect
+Deletion of semantically well-defined feature.
+\difficulty
+Syntactic transformation.
+\howwide
+Seldom.
+
 \rSec2[diff.class]{\ref{class}: classes}
 
 \diffref{class.name} [see also \ref{dcl.typedef}]
