CWG2753 Storage reuse for string literal objects and backing arrays

Author: burblebee

source/basic.tex

@@ -3300,6 +3300,12 @@
 standard-layout type\iref{basic.types.general} shall occupy contiguous bytes of
 storage.
 
+\pnum
+An object is a \defnadj{potentially non-unique}{object} if it is
+a string literal object\iref{lex.string},
+the backing array of an initializer list\iref{dcl.init.ref}, or
+a subobject thereof.
+
 \pnum
 \indextext{most derived object!bit-field}%
 \indextext{most derived object!zero size subobject}%
@@ -3312,7 +3318,9 @@
 if one is nested within the other,
 or
 if at least one is a subobject of zero size
-and they are of different types;
+and they are of different types,
+or
+if they are both potentially non-unique objects;
 otherwise, they have distinct addresses
 and occupy disjoint bytes of storage.
 \begin{footnote}
@@ -3326,6 +3334,14 @@
 static const char test1 = 'x';
 static const char test2 = 'x';
 const bool b = &test1 != &test2;        // always \tcode{true}
+
+static const char (&r) [] = "x";
+static const char *s = "x";
+static std::initializer_list<char> il = { 'x' };
+const bool b2 = r != il.begin();        // unspecified result
+const bool b3 = r != s;                 // unspecified result
+const bool b4 = il.begin() != &test1;   // always \tcode{true}
+const bool b5 = r != &test1;            // always \tcode{true}
 \end{codeblock}
 \end{example}
 The address of a non-bit-field subobject of zero size is

source/declarations.tex

@@ -6069,8 +6069,9 @@
 \end{note}
 If a narrowing conversion is required to initialize any of the elements,
 the program is ill-formed.
-Whether all backing arrays are distinct
-(that is, are stored in non-overlapping objects) is unspecified.
+\begin{note}
+Backing arrays are potentially non-unique objects\iref{intro.object}.
+\end{note}
 
 \pnum
 The backing array has the same lifetime as any other temporary

source/lex.tex

@@ -1955,11 +1955,12 @@
 \pnum
 Evaluating a \grammarterm{string-literal} results in a string literal object
 with static storage duration\iref{basic.stc}.
-\indextext{string!distinct}%
-Whether all \grammarterm{string-literal}s are distinct (that is, are stored in
-nonoverlapping objects) and whether successive evaluations of a
+\begin{note}
+String literal objects are potentially non-unique\iref{intro.object}.
+Whether successive evaluations of a
 \grammarterm{string-literal} yield the same or a different object is
 unspecified.
+\end{note}
 \begin{note}
 \indextext{literal!string!undefined change to}%
 The effect of attempting to modify a string literal object is undefined.