Annex C (informative) Compatibility [diff]

C.1 C++ and ISO C++ 2023 [diff.cpp23]

C.1.3 [dcl.dcl]: Declarations [diff.cpp23.dcl.dcl]

Affected subclause: [dcl.init.list]
Change: Pointer comparisons between initializer_list objects' backing arrays are unspecified.

Rationale: Permit the implementation to store backing arrays in static read-only memory.

Effect on original feature: Valid C++ 2023 code that relies on the result of pointer comparison between backing arrays may change behavior.
For example: bool ne(std::initializer_list<int> a, std::initializer_list<int> b) { return a.begin() != b.begin() + 1; } bool b = ne({2,3}, {1,2,3}); // unspecified result; previously false
Affected subclause: [dcl.array]
Change: Previously, T...[n] would declare a pack of function parameters.
T...[n] is now a pack-index-specifier.

Rationale: Improve the handling of packs.

Effect on original feature: Valid C++ 2023 code that declares a pack of parameters without specifying a declarator-id becomes ill-formed.
For example: template <typename... T> void f(T... [1]); template <typename... T> void g(T... ptr[1]); int main() { f<int, double>(nullptr, nullptr); // ill-formed, previously void f<int, double>(int [1], double [1]) g<int, double>(nullptr, nullptr); // ok }