// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf
#define msg "p274.cpp(129)11.3 Friends [class.friend]"

#include <iostream>

class X {
  int a;
  friend void friend_set(X*, int);
public:
  void member_set(int);
};
void friend_set(X* p, int i) {
  p->a = i;
}
void X::member_set(int i) {
  a = i;
}
void f() {
  X obj;
  friend_set(&obj,10);
  obj.member_set(10);
}

class A {
  class B { };
  friend class X3;
};
struct X3 : A::B { // OK: A::B accessible to friend
  A::B mx; // OK: A::B accessible to member of friend
  class Y {
    A::B my; // OK: A::B accessible to nested member of friend
  };
};


class X4 {
  enum { a=100 };
  friend class Y3;
};
class Y4 {
  int v[X4::a]; // OK, Y4 is a friend of X4
};
class Z4 {
  int v[X4::a]; // error: X4::a is private
};


class A3 {
  friend class B3 { }; // error: cannot define class in friend declaration
};


class C;
typedef C Ct;
class X1 {
  friend C; // OK: class C is a friend
};
class X2 {
  friend Ct; // OK: class C is a friend
  friend D; // error: no type-name D in scope
  friend class D; // OK: elaborated-type-specifier declares new class
};
template <typename T> class R {
  friend T;
};
R<C> rc; // class C is a friend of R<C>
R<int> Ri; // OK: "friend int;" is ignored


class Y5 {
  friend char* X5::foo(int);
friend X5:
  X5(char); // constructors can be friends
  friend X5::~X5(); // destructors can be friends
};


class M {
  friend void f3() { } // definition of global f, a friend of M,
// not the definition of a member function
};


class A6 {
  friend class B6;
  int a;
};
class B6 {
  friend class C6;
};
class C6 {
  void f(A6* p) {
    p->a++; // error: C is not a friend of A6
// despite being a friend of a friend
  }
};
class D6 : public B6 {
  void f(A6* p) {
    p->a++; // error: D6 is not a friend of A6
// despite being derived from a friend
  }
};


class X7;
void a();
void f2() {
  class Y7;
  extern void b();
  class A7 {
    friend class X7; // OK, but X is a local class, not ::X7
    friend class Y7; // OK
    friend class Z7; // OK, introduces local class Z7
    friend void a(); // error, ::a is not considered
    friend void b(); // OK
    friend void c(); // error
  };
  X7* px; // OK, but ::X7 is found
  Z7* pz; // error, no 7Z is found
}

int main() {
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p129
$ clang++ p129.cpp
p129.cpp:38:11: error: 'a' is a private member of 'X4'
int v[X4::a]; // OK, Y4 is a friend of X4
          ^
p129.cpp:34:8: note: implicitly declared private here
enum { a=100 };
       ^
p129.cpp:41:11: error: 'a' is a private member of 'X4'
int v[X4::a]; // error: X4::a is private
          ^
p129.cpp:34:8: note: implicitly declared private here
enum { a=100 };
       ^
p129.cpp:46:17: error: cannot define a type in a friend declaration
friend class B3 { }; // error: cannot define class in friend declaration
~~~~~~          ^
p129.cpp:57:8: error: C++ requires a type specifier for all declarations
friend D; // error: no type-name D in scope
~~~~~~ ^
p129.cpp:57:8: error: friends can only be classes or functions
p129.cpp:68:14: error: use of undeclared identifier 'X5'
friend char* X5::foo(int);
             ^
p129.cpp:69:8: error: unknown type name 'X5'
friend X5:X5(char); // constructors can be friends
       ^
p129.cpp:69:18: error: expected '(' for function-style cast or type construction
friend X5:X5(char); // constructors can be friends
             ~~~~^
p129.cpp:69:10: error: friends can only be classes or functions
friend X5:X5(char); // constructors can be friends
         ^
p129.cpp:70:8: error: use of undeclared identifier 'X5'
friend X5::~X5(); // destructors can be friends
       ^
p129.cpp:89:4: error: 'a' is a private member of 'A6'
p->a++; // error: C is not a friend of A6
   ^
p129.cpp:82:5: note: implicitly declared private here
int a;
    ^
p129.cpp:95:4: error: 'a' is a private member of 'A6'
p->a++; // error: D6 is not a friend of A6
   ^
p129.cpp:82:5: note: implicitly declared private here
int a;
    ^
p129.cpp:110:13: error: no matching function 'a' found in local scope; did you mean '::a'?
friend void a(); // error, ::a is not considered
            ^
            ::a
p129.cpp:102:6: note: '::a' declared here
void a();
     ^
p129.cpp:112:13: error: no matching function found in local scope
friend void c(); // error
            ^
p129.cpp:115:1: error: unknown type name 'Z7'
Z7* pz; // error, no 7Z is found
^
15 errors generated.

$ g++-7 p129.cpp
p129.cpp:38:11: error: 'X4::<unnamed enum> a' is private within this context
 int v[X4::a]; // OK, Y4 is a friend of X4
           ^
p129.cpp:34:8: note: declared private here
 enum { a=100 };
        ^
p129.cpp:41:11: error: 'X4::<unnamed enum> a' is private within this context
 int v[X4::a]; // error: X4::a is private
           ^
p129.cpp:34:8: note: declared private here
 enum { a=100 };
        ^
p129.cpp:46:1: error: class definition may not be declared a friend
 friend class B3 { }; // error: cannot define class in friend declaration
 ^~~~~~
p129.cpp:57:8: error: 'D' does not name a type
 friend D; // error: no type-name D in scope
        ^
p129.cpp:68:14: error: 'X5' has not been declared
 friend char* X5::foo(int);
              ^~
p129.cpp:69:8: error: 'X5' does not name a type; did you mean 'Y5'?
 friend X5:X5(char); // constructors can be friends
        ^~
        Y5
p129.cpp:70:8: error: 'X5' does not name a type; did you mean 'Y5'?
 friend X5::~X5(); // destructors can be friends
        ^~
        Y5
p129.cpp: In member function 'void C6::f(A6*)':
p129.cpp:89:4: error: 'int A6::a' is private within this context
 p->a++; // error: C is not a friend of A6
    ^
p129.cpp:82:5: note: declared private here
 int a;
     ^
p129.cpp: In member function 'void D6::f(A6*)':
p129.cpp:95:4: error: 'int A6::a' is private within this context
 p->a++; // error: D6 is not a friend of A6
    ^
p129.cpp:82:5: note: declared private here
 int a;
     ^
p129.cpp: In function 'void f2()':
p129.cpp:110:15: error: friend declaration 'void a()' in local class without prior declaration
 friend void a(); // error, ::a is not considered
               ^
p129.cpp:112:15: error: friend declaration 'void c()' in local class without prior declaration
 friend void c(); // error
               ^
p129.cpp:115:1: error: 'Z7' was not declared in this scope
 Z7* pz; // error, no 7Z is found
 ^~
p129.cpp:115:5: error: 'pz' was not declared in this scope
 Z7* pz; // error, no 7Z is found
     ^~
p129.cpp:115:5: note: suggested alternative: 'px'
 Z7* pz; // error, no 7Z is found
     ^~
     px