C++N4606(242)20.3 Compile-time integer sequences [intseq] 20.3.1 In general [intseq.general]p540


#はじめに(Introduction)
C++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

C++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(sequence)
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。

## C++N4606符号断片編纂一覧(example code compile list)
C++N4606 Working Draft 2016, ISO/IEC 14882, C++ standard(1) Example code compile list
https://qiita.com/kaizen_nagoya/items/df5d62c35bd6ed1c3d43/


## 編纂器(Compiler)
###clang++ --version
clang version 6.0.0 (tags/RELEASE_600/final)
Target: x86_64-apple-darwin17.4.0

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

#(242)20.3.1 In general [intseq.general]p540
##算譜(source code)

```c++:p540.cpp
// C++N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf
#define msg "C++N4606(242)20.3.1 In general [intseq.general]p540.cpp"
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>
#include <cstdlib>
#include <utility> // for index_sequence

//20.3 Compile-time integer sequences [intseq]
//20.3.1 In general [intseq.general]

template<class F, class Tuple, std::size_t... I>
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) { ///add std:: to index_sequence for clang++
  return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
}
template<class F, class Tuple>
decltype(auto) apply(F&& f, Tuple&& t) {
  using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>; ///add std:: to make_index_sequence for clang++
  return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
}
//20.3.2 Class template integer_sequence [intseq.intseq]
namespace std {
template<class T, T... I>
struct integer_sequence {
  using value_type = T;
  static constexpr size_t size() noexcept {
    return sizeof...(I);
  }
};
}

int main() {
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}
```
##編纂・実行結果(compile and go)

```shell_session:cppall.sh
$ ./cppall.sh p540
$ clang++ p540.cpp -std=c++03 -Wall
p540.cpp:13:43: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class F, class Tuple, std::size_t... I>
                                          ^
p540.cpp:14:10: warning: 'decltype(auto)' type specifier is a C++14 extension [-Wc++14-extensions]
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
         ^
p540.cpp:14:28: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
                           ^
p540.cpp:14:39: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
                                      ^
p540.cpp:14:50: error: no template named 'index_sequence' in namespace 'std'
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
                                            ~~~~~^
p540.cpp:14:1: error: 'decltype(auto)' not allowed in function return type
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
^~~~~~~~~~~~~~
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/__config:821:25: note: expanded from macro 'decltype'
#  define decltype(__x) __decltype(__x)
                        ^~~~~~~~~~
p540.cpp:18:10: warning: 'decltype(auto)' type specifier is a C++14 extension [-Wc++14-extensions]
decltype(auto) apply(F&& f, Tuple&& t) {
         ^
p540.cpp:18:23: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
decltype(auto) apply(F&& f, Tuple&& t) {
                      ^
p540.cpp:18:34: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
decltype(auto) apply(F&& f, Tuple&& t) {
                                 ^
p540.cpp:18:1: error: 'decltype(auto)' not allowed in function return type
decltype(auto) apply(F&& f, Tuple&& t) {
^~~~~~~~~~~~~~
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/__config:821:25: note: expanded from macro 'decltype'
#  define decltype(__x) __decltype(__x)
                        ^~~~~~~~~~
p540.cpp:19:17: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                ^
p540.cpp:19:22: error: no template named 'make_index_sequence' in namespace 'std'
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                ~~~~~^
p540.cpp:19:47: error: no template named 'tuple_size_v' in namespace 'std'; did you mean 'tuple_size'?
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                         ~~~~~^~~~~~~~~~~~
                                              tuple_size
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/__tuple:25:49: note: 'tuple_size' declared here
template <class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_size;
                                                ^
p540.cpp:19:65: error: no template named 'decay_t' in namespace 'std'; did you mean 'decay'?
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                                           ~~~~~^~~~~~~
                                                                decay
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/type_traits:1351:29: note: 'decay' declared here
struct _LIBCPP_TEMPLATE_VIS decay
                            ^
p540.cpp:19:78: error: a space is required between consecutive right angle brackets (use '> >')
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                                                             ^~
                                                                             > > 
p540.cpp:20:63: error: use of undeclared identifier 'Indices'
return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
                                                              ^
p540.cpp:24:20: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class T, T... I>
                   ^
p540.cpp:26:20: warning: alias declarations are a C++11 extension [-Wc++11-extensions]
using value_type = T;
                   ^
p540.cpp:27:8: error: unknown type name 'constexpr'
static constexpr size_t size() noexcept { return sizeof...(I); }
       ^
p540.cpp:27:24: error: expected ';' at end of declaration list
static constexpr size_t size() noexcept { return sizeof...(I); }
                       ^
                       ;
10 warnings and 10 errors generated.
$ clang++ p540.cpp -std=c++11 -Wall
p540.cpp:14:10: warning: 'decltype(auto)' type specifier is a C++14 extension [-Wc++14-extensions]
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
         ^
p540.cpp:14:50: error: no template named 'index_sequence' in namespace 'std'
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
                                            ~~~~~^
p540.cpp:14:1: error: deduced return types are a C++14 extension
decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
^
p540.cpp:18:10: warning: 'decltype(auto)' type specifier is a C++14 extension [-Wc++14-extensions]
decltype(auto) apply(F&& f, Tuple&& t) {
         ^
p540.cpp:18:1: error: deduced return types are a C++14 extension
decltype(auto) apply(F&& f, Tuple&& t) {
^
p540.cpp:19:22: error: no template named 'make_index_sequence' in namespace 'std'
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                ~~~~~^
p540.cpp:19:47: error: no template named 'tuple_size_v' in namespace 'std'; did you mean 'tuple_size'?
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                         ~~~~~^~~~~~~~~~~~
                                              tuple_size
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/__tuple:25:49: note: 'tuple_size' declared here
template <class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_size;
                                                ^
p540.cpp:19:65: error: no template named 'decay_t' in namespace 'std'; did you mean 'decay'?
using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                                           ~~~~~^~~~~~~
                                                                decay
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/type_traits:1351:29: note: 'decay' declared here
struct _LIBCPP_TEMPLATE_VIS decay
                            ^
p540.cpp:20:63: error: use of undeclared identifier 'Indices'
return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
                                                              ^
2 warnings and 7 errors generated.
$ clang++ p540.cpp -std=c++17 -Wall
C++N4606(242)20.3.1 In general [intseq.general]p540.cpp

$ g++-7 p540.cpp -std=c++03  -Wall
p540.cpp:14:1: warning: identifier 'decltype' is a keyword in C++11 [-Wc++11-compat]
 decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
 ^~~~~~~~
p540.cpp:27:1: warning: identifier 'constexpr' is a keyword in C++11 [-Wc++11-compat]
 static constexpr size_t size() noexcept { return sizeof...(I); }
 ^~~~~~
p540.cpp:27:1: warning: identifier 'noexcept' is a keyword in C++11 [-Wc++11-compat]
p540.cpp:13:47: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class F, class Tuple, std::size_t... I>
                                               ^
p540.cpp:14:10: warning: 'auto' changes meaning in C++11; please remove it [-Wc++11-compat]
 decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
          ^~~~
p540.cpp:14:10: error: ISO C++ forbids declaration of 'parameter' with no type [-fpermissive]
p540.cpp:14:16: error: expected constructor, destructor, or type conversion before 'apply_impl'
 decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
                ^~~~~~~~~~
p540.cpp:18:10: warning: 'auto' changes meaning in C++11; please remove it [-Wc++11-compat]
 decltype(auto) apply(F&& f, Tuple&& t) {
          ^~~~
p540.cpp:18:10: error: ISO C++ forbids declaration of 'parameter' with no type [-fpermissive]
p540.cpp:18:16: error: expected constructor, destructor, or type conversion before 'apply'
 decltype(auto) apply(F&& f, Tuple&& t) {
                ^~~~~
p540.cpp:24:24: warning: variadic templates only available with -std=c++11 or -std=gnu++11
 template<class T, T... I>
                        ^
p540.cpp:26:7: error: expected nested-name-specifier before 'value_type'
 using value_type = T;
       ^~~~~~~~~~
p540.cpp:27:8: error: 'constexpr' does not name a type
 static constexpr size_t size() noexcept { return sizeof...(I); }
        ^~~~~~~~~
p540.cpp:27:8: note: C++11 'constexpr' only available with -std=c++11 or -std=gnu++11

$ g++-7 p540.cpp -std=c++11  -Wall
p540.cpp:14:10: error: expected primary-expression before 'auto'
 decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
          ^~~~
p540.cpp:14:10: error: expected ')' before 'auto'
p540.cpp:14:1: error: expected unqualified-id before 'decltype'
 decltype(auto) apply_impl(F&& f, Tuple&& t, std::index_sequence<I...>) {
 ^~~~~~~~
p540.cpp:18:10: error: expected primary-expression before 'auto'
 decltype(auto) apply(F&& f, Tuple&& t) {
          ^~~~
p540.cpp:18:10: error: expected ')' before 'auto'
p540.cpp:18:1: error: expected unqualified-id before 'decltype'
 decltype(auto) apply(F&& f, Tuple&& t) {
 ^~~~~~~~

$ g++-7 p540.cpp -std=c++17  -Wall
p540.cpp: In function 'decltype(auto) apply(F&&, Tuple&&)':
p540.cpp:19:47: error: 'tuple_size_v' is not a member of 'std'
 using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                               ^~~~~~~~~~~~
p540.cpp:19:47: note: suggested alternative: 'tuple_size'
 using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                               ^~~~~~~~~~~~
                                               tuple_size
p540.cpp:19:78: error: template argument 1 is invalid
 using Indices = std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>;
                                                                              ^~
p540.cpp:20:63: error: there are no arguments to 'Indices' that depend on a template parameter, so a declaration of 'Indices' must be available [-fpermissive]
 return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
                                                               ^~~~~~~
p540.cpp:20:63: note: (if you use '-fpermissive', G++ will accept your code, but allowing the use of an undeclared name is deprecated)
p540.cpp: At global scope:
p540.cpp:25:8: error: redefinition of 'struct std::integer_sequence<_Tp, _Idx>'
 struct integer_sequence {
        ^~~~~~~~~~~~~~~~
In file included from p540.cpp:8:0:
/usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/utility:323:12: note: previous definition of 'struct std::integer_sequence<_Tp, _Idx>'
     struct integer_sequence
            ^~~~~~~~~~~~~~~~
```

#検討事項(agenda)
clang++ -std=c++17だけエラーなしの背景。
役に立つまたは意味のある出力

#参考資料(reference)

N4606 Working Draft 2016, ISO/IEC 14882, C++ standardのコード断片をコンパイルするためにしていること
https://qiita.com/kaizen_nagoya/items/a8d7ee2f2e29e76c19c1

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

C++2003とC++2017でコンパイルエラーになるならない事例集
https://qiita.com/kaizen_nagoya/items/a13ea3823441c430edff

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

cpprefjpのdecltypeをコンパイル試験
https://qiita.com/kaizen_nagoya/items/090909af702f0d5d8a67

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

「C++完全理解ガイド」の同意できること上位10
https://qiita.com/kaizen_nagoya/items/aa5744e0c4a8618c7671

#文書履歴(document history)
ver. 0.10 初稿 20180430
ver. 0.04 URL追記　20230307

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