// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf
#define msg "p263.cpp(124)10.3 Virtual functions [class.virtual]"

#include <iostream>

struct A {
virtual void f();
};
struct B : virtual A {
virtual void f();
};
struct C : B , virtual A {
using A::f;
};
void foo() {
C c;
c.f(); // calls B::f, the final overrider
c.C::f(); // calls A::f because of the using-declaration
}


struct A3 { virtual void f(); };
struct B3 : A3 { };
struct C3 : A3 { void f(); };
struct D3 : B3, C3 { }; // OK: A3::f and C3::f are the final overriders
// for the B3 and C3 subobjects, respectively

struct B4 {
virtual void f();
};
struct D4 : B4 {
void f(int);
};
struct D2 : D4 {
void f();
};

struct B5 {
virtual void f() const final;
};
struct D5 : B5 {
void f() const; // error: D::f attempts to override final B5::f
};

struct B6 {
virtual void f(int);
};
struct D6 : B6 {
virtual void f(long) override; // error: wrong signature overriding B6::f
virtual void f(int) override; // OK
};

class B7 { };
class D7 : private B7 { friend class Derived; };
struct Base {
virtual void vf1();
virtual void vf2();
virtual void vf3();
virtual B7* vf4();
virtual B7* vf5();
void f();
};
struct No_good : public Base {
D7* vf4(); // error: B7 (base class of D) inaccessible
};
class A7;
struct Derived : public Base {
void vf1(); // virtual and overrides Base::vf1()
void vf2(int); // not virtual, hides Base::vf2()
char vf3(); // error: invalid difference in return type only
D7* vf4(); // OK: returns pointer to derived class
A7* vf5(); // error: returns pointer to incomplete class
void f();
};
void g() {
Derived d;
Base* bp = &d; // standard conversion:
// Derived* to Base*
bp->vf1(); // calls Derived::vf1()
bp->vf2(); // calls Base::vf2()
bp->f(); // calls Base::f() (not virtual)
B7* p = bp->vf4(); // calls Derived::pf() and converts the
// result to B*
Derived* dp = &d;
D7* q = dp->vf4(); // calls Derived::pf() and does not
// convert the result to B7*
dp->vf2(); // ill-formed: argument mismatch
}

struct A8 {
virtual void f();
};
struct B1a : A8 { // note non-virtual derivation
void f();
};
struct B2a : A8 {
void f();
};
struct D8 : B1a, B2a { // D has two separate A subobjects
};
void foo2() {
D8 d;
// A8* ap = &d; // would be ill-formed: ambiguous
B1a* b1p = &d;
A8* ap = b1p;
D8* dp = &d;
ap->f(); // calls D8::B1a::f
dp->f(); // ill-formed: ambiguous
}

struct A9 {
virtual void f();
};
struct VB1 : virtual A9 { // note virtual derivation
void f();
};
struct VB2 : virtual A {
void f();
};
struct Error : VB1, VB2 { // ill-formed
};
struct Okay : VB1, VB2 {
void f();
};

struct VB1a : virtual A9 { // does not declare f
};
struct Da : VB1a, VB2 {
};
void foe() {
VB1a* vb1ap = new Da;
vb1ap->f(); // calls VB2::f
}

class B9 { public: virtual void f(); };
class D9 : public B9 { public: void f(); };
void D9::f() { /* ... */ B9::f(); }
int main(){
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p263
$ clang++ p263.cpp
p263.cpp:43:6: error: declaration of 'f' overrides a 'final' function
void f() const; // error: D::f attempts to override final B5::f
     ^
p263.cpp:40:14: note: overridden virtual function is here
virtual void f() const final;
             ^
p263.cpp:50:14: error: 'f' marked 'override' but does not override any member functions
virtual void f(long) override; // error: wrong signature overriding B6::f
             ^
p263.cpp:65:5: error: invalid covariant return for virtual function: 'B7' is a private base class of 'D7'
D7* vf4(); // error: B7 (base class of D) inaccessible
    ^
p263.cpp:55:12: note: declared private here
class D7 : private B7 { friend class Derived; };
           ^~~~~~~~~~
p263.cpp:71:6: error: virtual function 'vf3' has a different return type ('char') than the function it overrides
      (which has return type 'void')
char vf3(); // error: invalid difference in return type only
~~~~ ^
p263.cpp:59:14: note: overridden virtual function is here
virtual void vf3();
        ~~~~ ^
p263.cpp:73:5: error: return type of virtual function 'vf5' is not covariant with the return type of the function it overrides
      ('A7' is incomplete)
A7* vf5(); // error: returns pointer to incomplete class
    ^
p263.cpp:67:7: note: forward declaration of 'A7'
class A7;
      ^
p263.cpp:88:5: error: too few arguments to function call, expected 1, have 0; did you mean 'Base::vf2'?
dp->vf2(); // ill-formed: argument mismatch
    ^~~
    Base::vf2
p263.cpp:58:14: note: 'Base::vf2' declared here
virtual void vf2();
             ^
p263.cpp:109:5: error: member 'f' found in multiple base classes of different types
dp->f(); // ill-formed: ambiguous
    ^
p263.cpp:95:6: note: member found by ambiguous name lookup
void f();
     ^
p263.cpp:98:6: note: member found by ambiguous name lookup
void f();
     ^
7 errors generated.

$ g++-7 p263.cpp
p263.cpp:43:6: error: virtual function 'virtual void D5::f() const'
 void f() const; // error: D::f attempts to override final B5::f
      ^
p263.cpp:40:14: error: overriding final function 'virtual void B5::f() const'
 virtual void f() const final;
              ^
p263.cpp:50:14: error: 'virtual void D6::f(long int)' marked 'override', but does not override
 virtual void f(long) override; // error: wrong signature overriding B6::f
              ^
p263.cpp:65:5: error: invalid covariant return type for 'virtual D7* No_good::vf4()'
 D7* vf4(); // error: B7 (base class of D) inaccessible
     ^~~
p263.cpp:60:13: error:   overriding 'virtual B7* Base::vf4()'
 virtual B7* vf4();
             ^~~
p263.cpp:71:6: error: conflicting return type specified for 'virtual char Derived::vf3()'
 char vf3(); // error: invalid difference in return type only
      ^~~
p263.cpp:59:14: error:   overriding 'virtual void Base::vf3()'
 virtual void vf3();
              ^~~
p263.cpp:73:5: error: invalid covariant return type for 'virtual A7* Derived::vf5()'
 A7* vf5(); // error: returns pointer to incomplete class
     ^~~
p263.cpp:61:13: error:   overriding 'virtual B7* Base::vf5()'
 virtual B7* vf5();
             ^~~
p263.cpp: In function 'void g()':
p263.cpp:88:9: error: no matching function for call to 'Derived::vf2()'
 dp->vf2(); // ill-formed: argument mismatch
         ^
p263.cpp:70:6: note: candidate: void Derived::vf2(int)
 void vf2(int); // not virtual, hides Base::vf2()
      ^~~
p263.cpp:70:6: note:   candidate expects 1 argument, 0 provided
p263.cpp: In function 'void foo2()':
p263.cpp:109:5: error: request for member 'f' is ambiguous
 dp->f(); // ill-formed: ambiguous
     ^
p263.cpp:92:14: note: candidates are: virtual void A8::f()
 virtual void f();
              ^
p263.cpp:98:6: note:                 virtual void B2a::f()
 void f();
      ^
p263.cpp:95:6: note:                 virtual void B1a::f()
 void f();