This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115d. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2024-10-26
[Accepted as a DR as paper P3106R1 at the March, 2024 meeting.]
According to 9.4.2 [dcl.init.aggr] paragraph 4,
An array of unknown size initialized with a brace-enclosed initializer-list containing n initializer-clauses, where n shall be greater than zero, is defined as having n elements (9.3.4.5 [dcl.array]).
However, the interaction of this with brace elision is not clear. For instance, in the example in paragraph 7,
struct X { int i, j, k = 42; };
X a[] = { 1, 2, 3, 4, 5, 6 };
X b[2] = { { 1, 2, 3 }, { 4, 5, 6 } };
a and b are said to have the same value, even though there are six initializer-clauses in the initializer list in a's initializer and two in b's initializer.
Similarly, 13.10.3.2 [temp.deduct.call] paragraph 1 says,
in the P'[N] case, if N is a non-type template parameter, N is deduced from the length of the initializer list
Should that take into account the underlying type of the array? For example,
template<int N> void f1(const X(&)[N]);
f1({ 1, 2, 3, 4, 5, 6 }); // Is N deduced to 2 or 6?
template<int N> void f2(const X(&)[N][2]);
f2({ 1, 2, 3, 4, 5, 6 }); // Is N deduced to 1 or 6?
Additional notes (April, 2024)
The situation with arrays of unknown bound was clarified by P3106R1. The concern about template argument deduction was left untouched; the existing wording in 13.10.3.2 [temp.deduct.call] paragraph 1 seems to be clear, rendering the two examples shown above ill-formed, because deduction of P' against the integer arguments fails.