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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

N4606 Working Draft 2016, ISO/IEC 14882, C++ standard(63)6.8 Ambiguity resolution [stmt.ambig] p151

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#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。

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.

#(63)6.8 Ambiguity resolution [stmt.ambig]
p151

p151.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p151.cpp(63)6.8 Ambiguity resolution [stmt.ambig]"

#include <iostream>

T(a)->m = 7; // expression-statement
T(a)++; // expression-statement
T(a,5)<<c; // expression-statement
T(d)(int); // declaration
T(e)[5]; // declaration
T(f) = { 1, 2 }; // declaration
T(g)(double(3)); // declaration
class T {
  // ...
  public:
  T();
  T(int);
  T(int, int);
};
T(a); // declaration
T(*b)(); // declaration
T(c)=7; // declaration
T(d),e,f=3; // declaration
extern int h;
T(g)(h,2); // declaration
struct T1 {
  T1 operator()(int x) { return T1(x); }
  int operator=(int x) { return x; }
  T1(int) { }
};
struct T2 { T2(int){ } };
int a, ((*b)(T2))(int), c, d;
void f() {
  // disambiguation requires this to be parsed as a declaration:
  T1(a) = 3,
  T2(4), // T2 will be declared as
((*b)(T2(c)))(int(d)); // a variable of type T1
  // but this will not allow
  // the last part of the
  // declaration to parse
  // properly since it depends
  // on T2 being a type-name
}

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

$ ./cppgl17.sh p151
$ clang++ p151.cpp
p151.cpp:6:1: error: unknown type name 'T3'
T3(a3)->m = 7; // expression-statement
^
p151.cpp:6:7: error: expected ';' after top level declarator
T3(a3)->m = 7; // expression-statement
      ^
      ;
p151.cpp:7:1: error: unknown type name 'T3'
T3(a3)++; // expression-statement
^
p151.cpp:7:7: error: expected ';' after top level declarator
T3(a3)++; // expression-statement
      ^
      ;
p151.cpp:8:1: error: C++ requires a type specifier for all declarations
T3(a3,5)<<c; // expression-statement
^
p151.cpp:8:9: error: expected ';' after top level declarator
T3(a3,5)<<c; // expression-statement
        ^
        ;
p151.cpp:9:1: error: unknown type name 'T3'
T3(d3)(int); // declaration
^
p151.cpp:10:1: error: unknown type name 'T3'
T3(e3)[5]; // declaration
^
p151.cpp:11:1: error: unknown type name 'T3'
T3(f3) = { 1, 2 }; // declaration
^
p151.cpp:12:1: error: unknown type name 'T3'
T3(g3)(double(3)); // declaration
^
p151.cpp:32:15: error: function cannot return function type 'int (int)'
int a2, ((*b2)(T2))(int), c2, d2;
              ^
p151.cpp:35:5: warning: parentheses were disambiguated as redundant parentheses around declaration of variable named 'a2' [-Wvexing-parse]
  T1(a2) = 3,
    ^~~~
p151.cpp:35:3: note: add enclosing parentheses to perform a function-style cast
  T1(a2) = 3,
  ^
  (     )
p151.cpp:35:5: note: remove parentheses to silence this warning
  T1(a2) = 3,
    ^  ~
     
p151.cpp:37:8: error: must use 'struct' tag to refer to type 'T2' in this scope
((*b2)(T2(c2)))(int(d2)); // a variable of type T1
       ^
       struct 
p151.cpp:36:3: note: struct 'T2' is hidden by a non-type declaration of 'T2' here
  T2(4), // T2 will be declared as
  ^
p151.cpp:37:7: error: function cannot return function type 'T1 (int)'
((*b2)(T2(c2)))(int(d2)); // a variable of type T1
      ^
1 warning and 13 errors generated.

$ g++-7 p151.cpp
p151.cpp:6:3: error: expected constructor, destructor, or type conversion before '(' token
 T3(a3)->m = 7; // expression-statement
   ^
p151.cpp:7:3: error: expected constructor, destructor, or type conversion before '(' token
 T3(a3)++; // expression-statement
   ^
p151.cpp:8:3: error: expected constructor, destructor, or type conversion before '(' token
 T3(a3,5)<<c; // expression-statement
   ^
p151.cpp:9:3: error: expected constructor, destructor, or type conversion before '(' token
 T3(d3)(int); // declaration
   ^
p151.cpp:10:3: error: expected constructor, destructor, or type conversion before '(' token
 T3(e3)[5]; // declaration
   ^
p151.cpp:11:3: error: expected constructor, destructor, or type conversion before '(' token
 T3(f3) = { 1, 2 }; // declaration
   ^
p151.cpp:12:3: error: expected constructor, destructor, or type conversion before '(' token
 T3(g3)(double(3)); // declaration
   ^
p151.cpp:32:24: error: 'b2' declared as function returning a function
 int a2, ((*b2)(T2))(int), c2, d2;
                        ^
p151.cpp: In function 'void f2()':
p151.cpp:37:7: error: expected ')' before '(' token
 ((*b2)(T2(c2)))(int(d2)); // a variable of type T1
       ^

#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
https://qiita.com/kaizen_nagoya/items/f1a79a7cbd281607c7c9

#文書履歴
0.10 初稿 2080417

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