6 Statements [stmt.stmt]

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 parentheses86

( 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 range-based for statement is equivalent to

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

where __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:

• (1.1)

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

• (1.2)

  if _RangeT is a class type, the unqualified-ids begin and end are looked up in the scope of class _RangeT as if by class member access lookup ([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;

• (1.3)

  otherwise, begin-expr and end-expr are begin(__range) and end(__range), respectively, where begin and end are looked up with argument-dependent lookup ([basic.lookup.argdep]). For the purposes of this name lookup, namespace std is an associated namespace.

[ Example:

int array[5] = { 1, 2, 3, 4, 5 };
for (int& x : array)
  x *= 2;

 — end example ]

In the decl-specifier-seq of a for-range-declaration, each decl-specifier shall be either a type-specifier or constexpr.