Annex C (informative) Compatibility [diff]

C.5 C++ and ISO C++ 2017 [diff.cpp17]

C.5.4 [class]: classes [diff.cpp17.class]

Affected subclauses: [class.ctor], [class.conv.fct]
Change: The class name can no longer be used parenthesized immediately after an explicit decl-specifier in a constructor declaration.
The conversion-function-id can no longer be used parenthesized immediately after an explicit decl-specifier in a conversion function declaration.

Rationale: Necessary for new functionality.

Effect on original feature: Valid C++ 2017 code may fail to compile in this International Standard.
For example:
struct S {
  explicit (S)(const S&);       // ill-formed; previously well-formed
  explicit (operator int)();    // ill-formed; previously well-formed
  explicit(true) (S)(int);      // OK
};
Affected subclauses: [class.ctor], [class.dtor]
Change: A simple-template-id is no longer valid as the declarator-id of a constructor or destructor.

Rationale: Remove potentially error-prone option for redundancy.

Effect on original feature: Valid C++ 2017 code may fail to compile in this International Standard.
For example:
template<class T>
struct A {
  A<T>();          // error: simple-template-id not allowed for constructor
  A(int);          // OK, injected-class-name used
  ~A<T>();         // error: simple-template-id not allowed for destructor
};