Annex C (informative) Compatibility [diff]

Change: Removal of register storage-class-specifier.

Rationale: Enable repurposing of deprecated keyword in future revisions of C++.

Effect on original feature: A valid C++ 2014 declaration utilizing the register storage-class-specifier is ill-formed in this revision of C++.

The specifier can simply be removed to retain the original meaning.

Change: auto deduction from braced-init-list.

Rationale: More intuitive deduction behavior.

Effect on original feature: Valid C++ 2014 code may fail to compile or may change meaning in this revision of C++.

For example: auto x1{1}; // was std​::​initializer_list<int>, now int auto x2{1, 2}; // was std​::​initializer_list<int>, now ill-formed

Change: Make exception specifications be part of the type system.

Rationale: Improve type-safety.

Effect on original feature: Valid C++ 2014 code may fail to compile or change meaning in this revision of C++.

For example: void g1() noexcept; void g2(); template<class T> int f(T *, T *); int x = f(g1, g2); // ill-formed; previously well-formed

Change: Definition of an aggregate is extended to apply to user-defined types with base classes.

Rationale: To increase convenience of aggregate initialization.

Effect on original feature: Valid C++ 2014 code may fail to compile or produce different results in this revision of C++; initialization from an empty initializer list will perform aggregate initialization instead of invoking a default constructor for the affected types.

For example: struct derived; struct base { friend struct derived; private: base(); }; struct derived : base {}; derived d1{}; // error; the code was well-formed in C++ 2014 derived d2; // still OK