Annex C (informative) Compatibility [diff]

C.3 C++ and ISO C++ 2011 [diff.cpp11]

C.3.4 [dcl.dcl]: declarations [diff.cpp11.dcl.dcl]

Affected subclause: [dcl.constexpr]
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();
};
Affected subclause: [dcl.init.aggr]
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