// C++N4741 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n741.pdf
const char* msg= "C++N4741(208)17.6.6.2 Partial ordering of function templates [temp.func.order]p340.cpp";
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>
#include <cstdlib>

using namespace std;

namespace N {
  struct A { };
  template<class T> struct B {
    template<class R> int operator*(R&); // #1
  };
  template<class T, class R> int operator*(T&, R&); // #2
// The declaration of B::operator* is transformed into the equivalent of
// template<class R> int operator*(B<A>&, R&); // #1a
}

namespace M {
  template<class T> struct A {
    A();
  };
  template<class T> void f(T);
  template<class T> void f(T*);
  template<class T> void f(const T*);
  template<class T> void g(T);
  template<class T> void g(T&);
  template<class T> void h(const T&);
  template<class T> void h(A<T>&);
  void m() {
    const int* p;
    f(p); // f(const T*) is more specialized than f(T) or f(T*)
    float x;
    g(x); // ambiguous: g(T) or g(T&)
    A<int> z;
    h(z); // overload resolution selects h(A<T>&)
    const A<int> z2;
    h(z2); // h(const T&) is called because h(A<T>&) is not callable
  }
}

namespace P {
  template<class T> void f(T); // #1
  template<class T> void f(T*, int=1); // #2
  template<class T> void g(T); // #3
  template<class T> void g(T*, ...); // #4
}

namespace Q {
  template<class T, class U> struct A { };
  template<class T, class U> void f(U, A<U, T>* p = 0); // #1
  template< class U> void f(U, A<U, U>* p = 0); // #2
  template<class T > void g(T, T = T()); // #3
  template<class T, class... U> void g(T, U ...); // #4
  void h() {
    f<int>(42, (A<int, int>*)0); // calls #2
    f<int>(42); // error: ambiguous
    g(42); // error: ambiguous
  }
}

namespace R {
  template<class T, class... U> void f(T, U...); // #1
  template<class T > void f(T); // #2
  template<class T, class... U> void g(T*, U...); // #3
  template<class T > void g(T); // #4
  void h(int i) {
    f(&i); // error: ambiguous
    g(&i); // OK: calls #3
  }
}

int main() {
  N::A a;
  N::B<N::A> b;
  b * a; // calls #1a

  int* ip;
  P::f(ip); // calls #2
  P::g(ip); // calls #4

  cout << msg << endl;
  return EXIT_SUCCESS;
}

$ ../c1.sh p340
$ clang++ p340.cpp  -std=c++2a -Wall
p340.cpp:34:1: error: call to 'g' is ambiguous
g(x); // ambiguous: g(T) or g(T&)
^
p340.cpp:26:24: note: candidate function [with T = float]
template<class T> void g(T);
                       ^
p340.cpp:27:24: note: candidate function [with T = float]
template<class T> void g(T&);
                       ^
p340.cpp:57:1: error: call to 'f' is ambiguous
f<int>(42); // error: ambiguous
^~~~~~
p340.cpp:51:33: note: candidate function [with T = int, U = int]
template<class T, class U> void f(U, A<U, T>* p = 0); // #1
                                ^
p340.cpp:52:25: note: candidate function [with U = int]
template< class U> void f(U, A<U, U>* p = 0); // #2
                        ^
2 errors generated.

// C++N4741 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n741.pdf
const char* msg= "C++N4741(208)17.6.6.2 Partial ordering of function templates [temp.func.order]p340.cpp";
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>
#include <cstdlib>

using namespace std;

namespace N {
  struct A { };
  template<class T> struct B {
    template<class R> int operator*(R&) {
      return true;
    }; // #1///add {} for link error
  };
  template<class T, class R> int operator*(T&, R&); // #2
// The declaration of B::operator* is transformed into the equivalent of
// template<class R> int operator*(B<A>&, R&); // #1a
}

namespace M {
  template<class T> struct A {
    A() {};
  };///add {} for link error
  template<class T> void f(T) {}; ///add {} for link error
  template<class T> void f(T*);
  template<class T> void f(const T*) {}; ///add {} for link error
  template<class T> void g(T);
  template<class T> void g(T&);
  template<class T> void h(const T&) {}; ///add {} for link error
  template<class T> void h(A<T>&) {}; ///add {} for link error
  void m() {
    const int* p;
    f(p); // f(const T*) is more specialized than f(T) or f(T*)
    float x=9.9;/// add =9.9 for warning not initialized.
    cout << "x="<<x<<endl;/// add this line for warning not used.
///g(x); // ambiguous: g(T) or g(T&)
    A<int> z;
    h(z); // overload resolution selects h(A<T>&)
    const A<int> z2;
    h(z2); // h(const T&) is called because h(A<T>&) is not callable
  }
}

namespace P {
  template<class T> void f(T); // #1
  template<class T> void f(T*, int=1) {}; // #2///add {} for link error
  template<class T> void g(T); // #3
  template<class T> void g(T*, ...) {}; // #4///add {} for link error
}

namespace Q {
  template<class T, class U> struct A { };
  template<class T, class U> void f(U, A<U, T>* p = 0) {}; // #1///add {} for link error
  template< class U> void f(U, A<U, U>* p = 0) {}; // #2///add {} for link error
  template<class T > void g(T, T = T()) {}; // #3///add {} for link error
  template<class T, class... U> void g(T, U ...); // #4
  void h() {
    f<int>(42, (A<int, int>*)0); // calls #2
///f<int>(42); // error: ambiguous
    g(42); // error: ambiguous
  }
}

namespace R {
  template<class T, class... U> void f(T, U...); // #1
  template<class T > void f(T) {}; // #2///add {} for link error
  template<class T, class... U> void g(T*, U...) {}; // #3///add {} for link error
  template<class T > void g(T) {}; // #4///add {} for link error
  void h(int i) {
    f(&i); // error: ambiguous
    g(&i); // OK: calls #3
  }
}

int main() {
  N::A a;
  N::B<N::A> b;
  b * a; // calls #1a

  int* ip= nullptr;/// add null ptr for warning
  P::f(ip); // calls #2
  P::g(ip); // calls #4

  M::m();
  cout << msg << endl;
  return EXIT_SUCCESS;
}

$ ../cpla.sh p340a
$ clang++ p340a.cpp -std=c++03 -Wall
p340a.cpp:55:24: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class T, class... U> void g(T, U ...); // #4
                       ^
p340a.cpp:64:24: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class T, class... U> void f(T, U...); // #1
                       ^
p340a.cpp:66:24: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class T, class... U> void g(T*, U...){}; // #3///add {} for link error
                       ^
3 warnings generated.
x=9.9
C++N4741(208)17.6.6.2 Partial ordering of function templates [temp.func.order]p340.cpp
$ clang++ p340a.cpp -std=c++2a -Wall
x=9.9
C++N4741(208)17.6.6.2 Partial ordering of function templates [temp.func.order]p340.cpp

$ g++-8 p340a.cpp -std=c++03  -Wall
p340a.cpp:79:1: warning: identifier 'nullptr' is a keyword in C++11 [-Wc++11-compat]
 int* ip= nullptr;/// add null ptr for warning
 ^~~
p340a.cpp:55:24: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class T, class... U> void g(T, U ...); // #4
                        ^~~
p340a.cpp:55:43: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class T, class... U> void g(T, U ...); // #4
                                           ^~~
p340a.cpp:64:24: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class T, class... U> void f(T, U...); // #1
                        ^~~
p340a.cpp:64:42: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class T, class... U> void f(T, U...); // #1
                                          ^~~
p340a.cpp:66:24: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class T, class... U> void g(T*, U...){}; // #3///add {} for link error
                        ^~~
p340a.cpp:66:43: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class T, class... U> void g(T*, U...){}; // #3///add {} for link error
                                           ^~~
p340a.cpp: In function 'int main()':
p340a.cpp:77:3: error: ambiguous overload for 'operator*' (operand types are 'N::B<N::A>' and 'N::A')
 b * a; // calls #1a
 ~~^~~
p340a.cpp:14:23: note: candidate: 'int N::B<T>::operator*(R&) [with R = N::A; T = N::A]'
 template<class R> int operator*(R&){return true;}; // #1///add {} for link error
                       ^~~~~~~~
p340a.cpp:16:32: note: candidate: 'int N::operator*(T&, R&) [with T = N::B<N::A>; R = N::A]'
 template<class T, class R> int operator*(T&, R&); // #2
                                ^~~~~~~~
p340a.cpp:79:10: error: 'nullptr' was not declared in this scope
 int* ip= nullptr;/// add null ptr for warning
          ^~~~~~~

$ g++-8 p340a.cpp -std=c++2a  -Wall
p340a.cpp: In function 'int main()':
p340a.cpp:77:3: error: ambiguous overload for 'operator*' (operand types are 'N::B<N::A>' and 'N::A')
 b * a; // calls #1a
 ~~^~~
p340a.cpp:14:23: note: candidate: 'int N::B<T>::operator*(R&) [with R = N::A; T = N::A]'
 template<class R> int operator*(R&){return true;}; // #1///add {} for link error
                       ^~~~~~~~
p340a.cpp:16:32: note: candidate: 'int N::operator*(T&, R&) [with T = N::B<N::A>; R = N::A]'
 template<class T, class R> int operator*(T&, R&); // #2
                                ^~~~~~~~