P0683R1 Default member initializers for bit-fields

Author: zygoloid

source/classes.tex

@@ -467,7 +467,7 @@
 \nontermdef{member-declarator}\br
     declarator virt-specifier-seq\opt pure-specifier\opt\br
     declarator brace-or-equal-initializer\opt\br
-    identifier\opt attribute-specifier-seq\opt{} \terminal{:} constant-expression
+    identifier\opt{} attribute-specifier-seq\opt{} \terminal{:} constant-expression brace-or-equal-initializer\opt{}
 \end{bnf}
 
 \begin{bnf}
@@ -594,6 +594,26 @@
 \end{codeblock}
 \end{example}
 
+\pnum
+In a \grammarterm{member-declarator} for a bit-field,
+the \grammarterm{constant-expression} is parsed as
+the longest sequence of tokens
+that could syntactically form a \grammarterm{constant-expression}.
+\begin{example}
+\begin{codeblock}
+int a;
+const int b = 0;
+struct S {
+  int x1 : 8 = 42;               // OK, \tcode{"= 42"} is \grammarterm{brace-or-equal-initializer}
+  int x2 : 8 { 42 };             // OK, \tcode{"\{ 42 \}"} is \grammarterm{brace-or-equal-initializer}
+  int y1 : true ? 8 : a = 42;    // OK, \grammarterm{brace-or-equal-initializer} is absent
+  int y2 : true ? 8 : b = 42;    // error: cannot assign to \tcode{const int}
+  int y3 : (true ? 8 : b) = 42;  // OK, \tcode{"= 42"} is \grammarterm{brace-or-equal-initializer}
+  int z : 1 || new int { 0 };    // OK, \grammarterm{brace-or-equal-initializer} is absent
+};
+\end{codeblock}
+\end{example}
+
 \pnum
 A \grammarterm{brace-or-equal-initializer} shall appear only in the
 declaration of a data member. (For static data members,
@@ -1293,7 +1313,7 @@
 A \grammarterm{member-declarator} of the form
 
 \begin{ncbnftab}
-identifier\opt  attribute-specifier-seq\opt{} \terminal{:} constant-expression
+identifier\opt{} attribute-specifier-seq\opt{} \terminal{:} constant-expression brace-or-equal-initializer\opt{}
 \end{ncbnftab}
 
 \indextext{\idxcode{:}!bit-field declaration}%