This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

1274. Common nonterminal for expression and braced-init-list

[Moved to DR at the October, 2015 meeting.]

It would be helpful to have a single grammar term for expression and braced-init-list, which often occur together in the text. In particular, 8.6.5 [stmt.ranged] paragraph 1 allows both, but the description of __RangeT refers only to the expression case; such errors would be less likely if the common term were available.

Proposed resolution (May, 2015):

1. Add a new production to the grammar in 9.4 [dcl.init] paragraph 1:

expr-or-braced-init-list:
expression
braced-init-list

2. Change the grammar in 7.6.1 [expr.post] paragraph 1 as follows:

postfix-expression:
primary-expression
postfix-expression [ expression expr-or-braced-init-list ]
postfix-expression [ braced-init-list ]
postfix-expression ( expression-list_opt )
...

3. Change the grammar in 8.6 [stmt.iter] paragraph 1 as follows:

for-range-initializer:
expression
braced-init-list
expr-or-braced-init-list

4. Change 8.6.5 [stmt.ranged] paragraph 1 as follows:

For a range-based for statement of the form

for ( for-range-declaration : expression ) statement

let range-init be equivalent to the expression surrounded by parentheses⁹⁰

( expression )

and for a range-based for statement of the form

for ( for-range-declaration : braced-init-list ) statement

let range-init be equivalent to the braced-init-list. In each case, a A range-based for statement is equivalent to

  {
  auto && __range = range-init for-range-initializer;
    for ( auto __begin = begin-expr,
               __end = end-expr;
          __begin != __end;
          ++__begin ) {
      for-range-declaration = *__begin;
      statement
    }
  }

where

• if the for-range-initializer is an expression, it is regarded as if it were surrounded by parentheses (so that a comma operator cannot be reinterpreted as delimiting two init-declarators);

• __range, __begin, and __end are variables defined for exposition only,; and

• _RangeT is the type of the expression, and

• begin-expr and end-expr are determined as follows:

• if _RangeT the for-range-initializer is an expression of array type R, begin-expr and end-expr are __range and __range + __bound, respectively, where __bound is the array bound. If _RangeT R is an array of unknown size or an array of incomplete type, the program is ill-formed;

• if _RangeT the for-range-initializer is a an expression of class type C, the unqualified-ids begin and end are looked up in the scope of class _RangeT C as if by class member access lookup (_N4868_.6.5.6 [basic.lookup.classref]), and if either (or both) finds at least one declaration, begin-expr and end-expr are __range.begin() and __range.end(), respectively;

• otherwise, begin-expr and end-expr are begin(__range) and end(__range), respectively, where begin and end are looked up in the associated namespaces (6.5.4 [basic.lookup.argdep]). [Note: Ordinary unqualified lookup (6.5.3 [basic.lookup.unqual]) is not performed. —end note]

5. Change the grammar of 8.7 [stmt.jump] paragraph 1 as follows:

jump-statement:
break ;
continue ;
return expression expr-or-braced-init-list_opt ;
return braced-init-list ;
goto identifier ;

6. Change 8.7.4 [stmt.return] paragraph 2 as follows:

The expression or braced-init-list expr-or-braced-init-list of a return statement is called its operand. A return statement...

7. Change 12.4.5 [over.sub] paragraph 1 as follows:

operator[] shall be a non-static member function with exactly one parameter. It implements the subscripting syntax

postfix-expression [ expression expr-or-braced-init-list ]

or

postfix-expression [ braced-init-list ]

Thus, a subscripting expression...