C++ N4606 (81)7.3.4 Using directive [namespace.udir] p188

#はじめに
N4606 Working Draft, Standard for Programming Language C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/#mailing2016-11
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf

n4606は、ISO/IEC JTC1 SC22 WG21の作業原案(Working Draft)です。
公式のISO/IEC 14882原本ではありません。
ISO/IEC JTC1 SC22 WG21では、可能な限り作業文書を公開し、幅広い意見を求めています。
一連の記事はコード断片をコンパイルできる形にする方法を検討してコンパイル、リンク、実行して、規格案の原文と処理系(g++, Clang++)との違いを確認し、技術内容を検討し、ISO/IEC JTC1 SC22 WG21にフィードバックするために用います。
また、CERT C++, MISRA C++等のコーディング標準のコード断片をコンパイルする際の参考にさせていただこうと考えています。CERT C++, MISRA C++が標準化の動きとの時間的なずれがあれば確認できれば幸いです。また、boostライブラリとの関連、Linux OS, TOPPERSカーネル、g++(GCC), clang++(LLVM）との関係も調査中です。
何か、抜け漏れ、耳より情報がありましたらおしらせくださると幸いです。

##作業方針
１）コンパイルエラーを収集する。
２）コンパイルエラーをなくす方法を検討する。
コンパイルエラーになる例を示すだけが目的のコードは、コンパイルエラーをなくすのではなく、コンパイルエラーの種類を収集するだけにする。
文法を示すのが目的のコード場合に、コンパイルエラーをなくすのに手間がかかる場合は、順次作業します。
３）リンクエラーをなくす方法を検討する。
文法を示すのが目的のコード場合に、リンクエラーをなくすのに手間がかかる場合は、順次作業します。
４）意味のある出力を作る。
コンパイル、リンクが通っても、意味のある出力を示そうとすると、コンパイル・リンクエラーが出て収拾できそうにない場合がある。順次作業します。

１）だけのものから４）まで進んだものと色々ある状態です。一歩でも前に進むご助言をお待ちしています。「検討事項」の欄に現状を記録するようにしています。

## list
N4606 Working Draft 2016, ISO/IEC 14882, C++ standard(1) coding list
https://qiita.com/kaizen_nagoya/items/df5d62c35bd6ed1c3d43/


## Compiler
###clang++ --version
clang version 6.0.0 (tags/RELEASE_600/final)

###g++-7 --version
g++-7 (Homebrew GCC 7.3.0_1) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.

#(81)7.3.4 Using directive [namespace.udir]
p188

```c++:p188.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p188.cpp(81)7.3.4 Using directive [namespace.udir]"

#include <iostream>

namespace A {
  int i;
  namespace B {
    namespace C {
      int i;
    }
  using namespace A::B::C;
  void f1() {
    i = 5; // OK, C::i visible in B and hides A::i
    }
  }
  namespace D {
    using namespace B;
    using namespace C;
    void f2() {
      i = 5; // ambiguous, B::C::i or A::i?
    }
  }
  void f3() {
    i = 5; // uses A::i
  }
}
void f4() {
  i = 5; // ill-formed; neither i is visible
}
namespace M {
  int i;
}
namespace N {
  int i;
using namespace M;
}
void f() {
  using namespace N;
  i = 7; // error: both M::i and N::i are visible
}
namespace A {
  int i;
}
namespace B {
  int i;
  int j;
  namespace C {
  namespace D {
  using namespace A;
  int j;
  int k;
  int a = i; // B::i hides A::i
}
using namespace D;
int k = 89; // no problem yet
int l = k; // ambiguous: C::k or D::k
int m = i; // B::i hides A::i
int n = j; // D::j hides B::j
}
}
namespace A {
  class X { };
  extern "C" int g();
  extern "C++" int h();
}
namespace B {
  void X(int);
  extern "C" int g();
  extern "C++" int h(int);
}
using namespace A;
using namespace B;
void f() {
  X(1); // error: name X found in two namespaces
  g(); // OK: name g refers to the same entity
  h(); // OK: overload resolution selects A::h
}
namespace D {
  int d1;
  void f(char);
}
using namespace D;
int d1; // OK: no conflict with D::d1
namespace E {
  int e;
  void f(int);
}
namespace D { // namespace extension
  int d2;
  using namespace E;
  void f(int);
}
void f() {
  d1++; // error: ambiguous ::d1 or D::d1?
  ::d1++; // OK
  D::d1++; // OK
  d2++; // OK: D::d2
  e++; // OK: E::e
  f(1); // error: ambiguous: D::f(int) or E::f(int)?
  f('a'); // OK: D::f(char)
}
int main(){
  int i=1;
  foo(i);
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}
```

```shell_session
$ ./cppgl17.sh p188
$ clang++ p188.cpp
p188.cpp:22:7: error: reference to 'i' is ambiguous
      i = 5; // ambiguous, B::C::i or A::i?
      ^
p188.cpp:8:7: note: candidate found by name lookup is 'A::i'
  int i;
      ^
p188.cpp:11:11: note: candidate found by name lookup is 'A::B::C::i'
      int i;
          ^
p188.cpp:30:3: error: use of undeclared identifier 'i'; did you mean 'A::i'?
  i = 5; // ill-formed; neither i is visible
  ^
  A::i
p188.cpp:8:7: note: 'A::i' declared here
  int i;
      ^
p188.cpp:41:3: error: reference to 'i' is ambiguous
  i = 7; // error: both M::i and N::i are visible
  ^
p188.cpp:36:7: note: candidate found by name lookup is 'N::i'
  int i;
      ^
p188.cpp:33:7: note: candidate found by name lookup is 'M::i'
  int i;
      ^
p188.cpp:44:7: error: redefinition of 'i'
  int i;
      ^
p188.cpp:8:7: note: previous definition is here
  int i;
      ^
p188.cpp:58:9: error: reference to 'k' is ambiguous
int l = k; // ambiguous: C::k or D::k
        ^
p188.cpp:57:5: note: candidate found by name lookup is 'B::C::k'
int k = 89; // no problem yet
    ^
p188.cpp:53:7: note: candidate found by name lookup is 'B::C::D::k'
  int k;
      ^
p188.cpp:74:17: error: reference to 'B' is ambiguous
using namespace B;
                ^
p188.cpp:68:11: note: candidate found by name lookup is 'B'
namespace B {
          ^
p188.cpp:9:13: note: candidate found by name lookup is 'A::B'
  namespace B {
            ^
p188.cpp:75:6: error: redefinition of 'f'
void f() {
     ^
p188.cpp:39:6: note: previous definition is here
void f() {
     ^
p188.cpp:76:3: error: no matching conversion for functional-style cast from 'int' to 'A::X'
  X(1); // error: name X found in two namespaces
  ^~~
p188.cpp:64:9: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'int' to 'const A::X' for
      1st argument
  class X { };
        ^
p188.cpp:64:9: note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'int' to 'A::X' for 1st
      argument
  class X { };
        ^
p188.cpp:64:9: note: candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 1 was provided
p188.cpp:84:17: error: reference to 'D' is ambiguous
using namespace D;
                ^
p188.cpp:80:11: note: candidate found by name lookup is 'D'
namespace D {
          ^
p188.cpp:18:13: note: candidate found by name lookup is 'A::D'
  namespace D {
            ^
p188.cpp:98:3: error: reference to 'D' is ambiguous
  D::d1++; // OK
  ^
p188.cpp:90:11: note: candidate found by name lookup is 'D'
namespace D { // namespace extension
          ^
p188.cpp:18:13: note: candidate found by name lookup is 'A::D'
  namespace D {
            ^
p188.cpp:99:3: error: use of undeclared identifier 'd2'; did you mean 'D::d2'?
  d2++; // OK: D::d2
  ^~
  D::d2
p188.cpp:91:7: note: 'D::d2' declared here
  int d2;
      ^
p188.cpp:100:3: error: use of undeclared identifier 'e'; did you mean 'D::e'?
  e++; // OK: E::e
  ^
  D::e
p188.cpp:87:7: note: 'D::e' declared here
  int e;
      ^
p188.cpp:106:3: error: use of undeclared identifier 'foo'
  foo(i);
  ^
13 errors generated.

$ g++-7 p188.cpp
p188.cpp: In function 'void A::D::f2()':
p188.cpp:22:7: error: reference to 'i' is ambiguous
       i = 5; // ambiguous, B::C::i or A::i?
       ^
p188.cpp:8:7: note: candidates are: int A::i
   int i;
       ^
p188.cpp:11:11: note:                 int A::B::C::i
       int i;
           ^
p188.cpp: In function 'void f4()':
p188.cpp:30:3: error: 'i' was not declared in this scope
   i = 5; // ill-formed; neither i is visible
   ^
p188.cpp:30:3: note: suggested alternatives:
p188.cpp:8:7: note:   'A::i'
   int i;
       ^
p188.cpp:11:11: note:   'A::B::C::i'
       int i;
           ^
p188.cpp:11:11: note:   'A::B::C::i'
p188.cpp:11:11: note:   'A::B::C::i'
p188.cpp: In function 'void f()':
p188.cpp:41:3: error: reference to 'i' is ambiguous
   i = 7; // error: both M::i and N::i are visible
   ^
p188.cpp:33:7: note: candidates are: int M::i
   int i;
       ^
p188.cpp:36:7: note:                 int N::i
   int i;
       ^
p188.cpp: At global scope:
p188.cpp:44:7: error: redefinition of 'int A::i'
   int i;
       ^
p188.cpp:8:7: note: 'int A::i' previously declared here
   int i;
       ^
p188.cpp:58:9: error: reference to 'k' is ambiguous
 int l = k; // ambiguous: C::k or D::k
         ^
p188.cpp:57:5: note: candidates are: int B::C::k
 int k = 89; // no problem yet
     ^
p188.cpp:53:7: note:                 int B::C::D::k
   int k;
       ^
p188.cpp:74:17: error: reference to 'B' is ambiguous
 using namespace B;
                 ^
p188.cpp:46:11: note: candidates are: namespace B { }
 namespace B {
           ^
p188.cpp:9:13: note:                 namespace A::B { }
   namespace B {
             ^
p188.cpp:74:17: error: 'B' is not a namespace-name
 using namespace B;
                 ^
p188.cpp:74:18: error: expected namespace-name before ';' token
 using namespace B;
                  ^
p188.cpp: In function 'void f()':
p188.cpp:75:6: error: redefinition of 'void f()'
 void f() {
      ^
p188.cpp:39:6: note: 'void f()' previously defined here
 void f() {
      ^
p188.cpp:76:6: error: no matching function for call to 'A::X::X(int)'
   X(1); // error: name X found in two namespaces
      ^
p188.cpp:64:9: note: candidate: constexpr A::X::X()
   class X { };
         ^
p188.cpp:64:9: note:   candidate expects 0 arguments, 1 provided
p188.cpp:64:9: note: candidate: constexpr A::X::X(const A::X&)
p188.cpp:64:9: note:   no known conversion for argument 1 from 'int' to 'const A::X&'
p188.cpp:64:9: note: candidate: constexpr A::X::X(A::X&&)
p188.cpp:64:9: note:   no known conversion for argument 1 from 'int' to 'A::X&&'
p188.cpp: At global scope:
p188.cpp:84:17: error: reference to 'D' is ambiguous
 using namespace D;
                 ^
p188.cpp:80:11: note: candidates are: namespace D { }
 namespace D {
           ^
p188.cpp:18:13: note:                 namespace A::D { }
   namespace D {
             ^
p188.cpp:84:17: error: 'D' is not a namespace-name
 using namespace D;
                 ^
p188.cpp:84:18: error: expected namespace-name before ';' token
 using namespace D;
                  ^
p188.cpp: In function 'void f()':
p188.cpp:95:6: error: redefinition of 'void f()'
 void f() {
      ^
p188.cpp:39:6: note: 'void f()' previously defined here
 void f() {
      ^
p188.cpp:98:3: error: reference to 'D' is ambiguous
   D::d1++; // OK
   ^
p188.cpp:80:11: note: candidates are: namespace D { }
 namespace D {
           ^
p188.cpp:18:13: note:                 namespace A::D { }
   namespace D {
             ^
p188.cpp:99:3: error: 'd2' was not declared in this scope
   d2++; // OK: D::d2
   ^~
p188.cpp:99:3: note: suggested alternative:
p188.cpp:91:7: note:   'D::d2'
   int d2;
       ^~
p188.cpp:100:3: error: 'e' was not declared in this scope
   e++; // OK: E::e
   ^
p188.cpp:100:3: note: suggested alternatives:
p188.cpp:87:7: note:   'E::e'
   int e;
       ^
p188.cpp:87:7: note:   'E::e'
p188.cpp:101:6: error: too many arguments to function 'void f()'
   f(1); // error: ambiguous: D::f(int) or E::f(int)?
      ^
p188.cpp:39:6: note: declared here
 void f() {
      ^
p188.cpp:102:8: error: too many arguments to function 'void f()'
   f('a'); // OK: D::f(char)
        ^
p188.cpp:39:6: note: declared here
 void f() {
      ^
p188.cpp: In function 'int main()':
p188.cpp:106:3: error: 'foo' was not declared in this scope
   foo(i);
   ^~~
```

#検討事項
コンパイルエラーをなくす修正。

#参考資料

コンパイル用shell script C版(clangとgcc)とC++版(clang++とg++)
https://qiita.com/kaizen_nagoya/items/74220c0577a512c2d7da

Clang/Clang++(LLVM) gcc/g++(GNU) コンパイラ警告等比較
https://qiita.com/kaizen_nagoya/items/9a82b958cc3aeef0403f

Qiitaに投稿するCのStyle例(暫定)
https://qiita.com/kaizen_nagoya/items/946df1528a6a1ef2bc0d

MISRA C++ 5-0-16
https://qiita.com/kaizen_nagoya/items/7df2d4e05db724752a74

C++ Templates Part1 BASICS Chapter 3. Class Templates 3.2 Use of Class Template Stack stack1test.cpp
https://qiita.com/kaizen_nagoya/items/cd5fc49106fad5a4e9ed


ISO/IEC TS 17961:2013 C Secure Coding Rules(1) All list(to be confirmed)
https://qiita.com/kaizen_nagoya/items/54e056195c4f11b850a1

C言語（C++)に対する誤解、曲解、無理解、爽快。
https://qiita.com/kaizen_nagoya/items/3f3992c9722c1cee2e3a

C Puzzle Bookの有り難み5つ、C言語規格及びCコンパイラの特性を認識
https://qiita.com/kaizen_nagoya/items/d89a48c1536a02ecdec9

'wchar.h' file not found で困った clang++ macOS
https://qiita.com/kaizen_nagoya/items/de15cd46d657517fac11

Open POSIX Test Suiteの使い方を調べはじめました
https://qiita.com/kaizen_nagoya/items/644d5e407f5faf96e6dc

MISRA-C 2012 Referenceに掲載している文献の入手可能性を確認
https://qiita.com/kaizen_nagoya/items/96dc8b125e462d5575bb

どうやって MISRA Example Suiteをコンパイルするか
https://qiita.com/kaizen_nagoya/items/fbdbff5ff696e2ca7f00

MISRA C まとめ #include <misra_c.h>
https://qiita.com/kaizen_nagoya/items/f1a79a7cbd281607c7c9

#文書履歴
0.10 初稿 2080417