Annex C (informative) Compatibility [diff]

Change: constexpr non-static member functions are not implicitly const member functions.

Rationale: Necessary to allow constexpr member functions to mutate the object.

Effect on original feature: Valid C++ 2011 code may fail to compile in this International Standard.

For example, the following code is valid in C++ 2011 but invalid in this International Standard because it declares the same member function twice with different return types:

struct S {
  constexpr const int &f();
  int &f();
};

Change: Classes with default member initializers can be aggregates.

Rationale: Necessary to allow default member initializers to be used by aggregate initialization.

Effect on original feature: Valid C++ 2011 code may fail to compile or may change meaning in this International Standard.

For example:

struct S {          // Aggregate in C++ 2014 onwards.
  int m = 1;
};
struct X {
  operator int();
  operator S();
};
X a{};
S b{a};             // uses copy constructor in C++ 2011,
                    // performs aggregate initialization in this International Standard