22.10.15 Function object binders [func.bind] C++N4910:2022 (625) p754.cpp

# はじめに(Introduction)

N4910  Working Draft, Standard for Programming Language C++

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/n4910.pdf

n4910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。

 <この項は書きかけです。順次追記します。>

## 背景(back ground)
C/C++でコンパイルエラーが出ると、途方にくれることがしばしばあります。
何回かに１回は、該当するエラーが検索できます。
ただ、条件が違っていて、そこでの修正方法では目的を達成しないこともしばしばです。いろいろな条件のコンパイルエラーとその対応方法について、広く記録することによって、いつか同じエラーに遭遇した時にやくに立つことを目指しています。

この半年の間で、三度、自分のネットでの記録に助けられたことがあります。
また過去に解決できなかった記録を１０種類以上、最近になって解決できたことがあります。それは、主に次の３つの情報に基づいています。

https://stackoverflow.com

http://ja.cppreference.com/

cpprefjp - C++日本語リファレンス

https://cpprefjp.github.io/

コンパイラの実装状況

https://cpprefjp.github.io/implementation-status.html

また
https://researchmap.jp/joub9b3my-1797580/#_1797580
に記載したサイトのお世話になっています。

## 作業方針(sequence)
Clang++では-std=c++03, C++2bの2種類
g++では-std=c++03, c++2bの２種類
でコンパイルし、

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++N4910:2022 Standard Working Draft on ISO/IEC 14882(0) sample code compile list  

https://qiita.com/kaizen_nagoya/items/fc957ddddd402004bb91

### C++N4741, 2018 Standard Working Draft on ISO/IEC 14882 sample code compile list
https://qiita.com/kaizen_nagoya/items/3294c014044550896010

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

### C++N3242, 2011 sample code compile list on clang++ and g++
https://qiita.com/kaizen_nagoya/items/685b5c1a2c17c1bf1318

## 編纂器(Compiler)
### clang++ --version
> Debian clang version 14.0.5-++20220610033153+c12386ae247c-1~exp1~20220610153237.151
Target: x86_64-pc-linux-gnu, Thread model: posix, InstalledDir: /usr/bin

### g++- --version
> g++ (GCC) 12.1.0  Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# 22.10.15 Function object binders [func.bind] C++N4910:2022 (625) p754.cpp

## 算譜(source code)

```c++:p754.cpp
// C++N4910 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/n4910.pdf
const char * n4910 = "22.10.15 Function object binders [func.bind] C++N4910:2022 (625) p754.cpp";
// Debian clang version 14.0.5-++20220610033153+c12386ae247c-
// g++ (GCC) 12.1.0 Copyright (C) 2022 Free Software Foundation, Inc.
// Edited by Dr. OGAWA Kiyoshi. Compile procedure and results record.
// C++N4910:2022 Standard Working Draft on ISO/IEC 14882(0) sample code compile list
// https://qiita.com/kaizen_nagoya/items/fc957ddddd402004bb91

#include "N4910.h"

using namespace std;


// 22.10.15.1 General [func.bind.general]
// Subclause 22.10.15 describes a uniform mechanism for binding arguments of callable objects.
// 22.10.15.2 Class template is_bind_expression [func.bind.isbind]
namespace std {
template<class T> struct is_bind_expression; // see below
}
//  The class template is_bind_expression can be used to detect function objects generated by bind. The function template bind uses is_bind_expression to detect subexpressions.
//  Specializations of the is_bind_expression template shall meet the Cpp17UnaryTypeTrait requirements (21.3.2). The implementation provides a definition that has a base characteristic of true_type if T is a type returned from bind, otherwise it has a base characteristic of false_type. A program may specialize this template for a program-defined type T to have a base characteristic of true_type to indicate that T should be treated as a subexpression in a bind call.
// 22.10.15.3 Class template is_placeholder [func.bind.isplace]
namespace std {
template<class T> struct is_placeholder; // see below
}
//  The class template is_placeholder can be used to detect the standard placeholders _1, _2, and so on. The function template bind uses is_placeholder to detect placeholders.
//  Specializations of the is_placeholder template shall meet the Cpp17UnaryTypeTrait requirements (21.3.2). The implementation provides a definition that has the base characteristic of integral_constant<int, J > if T is the type of std::placeholders::_J , otherwise it has a base characteristic of integral_constant<int, 0>. A program may specialize this template for a program-defined type T to have a base characteristic of integral_constant<int, N> with N > 0 to indicate that T should be treated as a placeholder type.
// 22.10.15.4 Function template bind [func.bind.bind]
//  In the text that follows:
// — g is a value of the result of a bind invocation,
// — FD is the type decay_t<F>,
// — fd is an lvalue that is a target object of g (22.10.3) of type FD direct-non-list-initialized with std::forward<F>(f),
// — Ti is the ith type in the template parameter pack BoundArgs,
// — TDi is the type decay_t<Ti>,
// — ti is the ith argument in the function parameter pack bound_args,
// — tdi is a bound argument entity of g (22.10.3) of type TDi direct-non-list-initialized with std::forward< Ti >(ti ),
// — Uj is the jth deduced type of the UnBoundArgs&&... parameter of the argument forwarding call wrapper, and
// — uj is the jth argument associated with Uj.
static_cast<cv TDi &>(tdi )(std::forward<Uj >(uj )...)
// and its type Vi is invoke_result_t<cv TDi&, Uj...>&&;
//— if the value j of is_placeholder_v<TDi> is not zero, the argument is std::forward<Uj>(uj) and its type Vi is Uj&&;
//Mandates: is_constructible_v<FD, F> is true. For each Ti in BoundArgs, is_constructible_- v<TDi, Ti> is true.
//Preconditions: FD and each TDi meet the Cpp17MoveConstructible and Cpp17Destructible requirements. INVOKE(fd, w1, w2, . . . , wN ) (22.10.4) is a valid expression for some values w1, w2, . . . , wN , where N has the value sizeof...(bound_args).
//Returns: An argument forwarding call wrapper g (22.10.4). A program that attempts to invoke a volatile-qualified g is ill-formed. When g is not volatile-qualified, invocation of g(u1, u2, . . . , uM ) is expression-equivalent (3.21) to
INVOKE(static_cast<Vfd >(vfd ),
       static_cast<V1>(v1), static_cast<V2>(v2), ..., static_cast<VN>(vN))
//for the first overload, and
INVOKE<R>(static_cast<Vfd >(vfd ),
          static_cast<V1>(v1), static_cast<V2>(v2), ..., static_cast<VN>(vN))
//for the second overload, where the values and types of the target argument vfd and of the bound argumentsv1,v2,...,vN aredeterminedasspecifiedbelow.
// Throws: Any exception thrown by the initialization of the state entities of g.
// [Note 1: If all of FD and TDi meet the requirements of Cpp17CopyConstructible, then the return type meets the
template<class F, class... BoundArgs>
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
template<class R, class F, class... BoundArgs>
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
// requirements of Cpp17CopyConstructible.
// The values of the bound arguments v1, v2, . . . , vN and their corresponding types V1, V2, . . . , VN depend on the types TDi derived from the call to bind and the cv-qualifiers cv of the call wrapper g as follows:
// — if TDi is reference_wrapper<T>, the argument is tdi.get() and its type Vi is T&;
// — if the value of is_bind_expression_v<TDi> is true, the argument is
// — otherwise, the value is tdi and its type Vi is cv TDi
//  The value of the target argument vfd is fd and its corresponding type Vfd is cv FD&
// 22.10.15.5 Placeholders [func.bind.place]
namespace std::placeholders {
// M is the implementation-defined number of placeholders
see_below_1;
see_below_2;
see_below_M;
}
//  The value of the target argument vfd is fd and its corresponding type Vfd is cv FD&.
//  All placeholder types meet the Cpp17DefaultConstructible and Cpp17CopyConstructible requirements, and their default constructors and copy/move constructors are constexpr functions that do not throw exceptions.
// Returns: An implementation-defined ntbs.
// It is implementation-defined whether placeholder types meet the Cpp17CopyAssignable requirements, but if so, their copy assignment operators are constexpr functions that do not throw exceptions.
//  Placeholders should be defined as:
inline constexpr unspecified _1{};
// If they are not, they are declared as:
extern unspecified _1;
int main() {
    cout  <<  n4910 << endl;
    return EXIT_SUCCESS;
}
```

## 編纂・実行結果(compile and go)

```ubuntu:bash
$ clang++ p754.cpp -std=03 -o p754l -I. -Wall
In file included from p754.cpp:10:
In file included from ./N4910.h:11:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/atomic:38:
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/c++0x_warning.h:32:2: error: This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
#error This file requires compiler and library support \
 ^
p754.cpp:40:1: error: expected unqualified-id
static_cast<cv TDi &>(tdi )(std::forward<Uj >(uj )...) 
^
p754.cpp:56:33: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class R, class F, class... BoundArgs>
                                ^
p754.cpp:57:1: error: unknown type name 'constexpr'
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
^
p754.cpp:57:11: warning: variable templates are a C++14 extension [-Wc++14-extensions]
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
          ^
p754.cpp:57:22: error: expected ';' at end of declaration
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
                     ^
                     ;
p754.cpp:57:28: error: unknown type name 'F'
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
                           ^
p754.cpp:57:29: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
                            ^
p754.cpp:57:35: error: unknown type name 'BoundArgs'
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
                                  ^
p754.cpp:57:44: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
                                           ^
p754.cpp:57:46: error: type 'int &&' of function parameter pack does not contain any unexpanded parameter packs
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
                                  ~~~~~~~~~~~^~~~~~~~~~~~~~
p754.cpp:57:23: error: C++ requires a type specifier for all declarations
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
                      ^
p754.cpp:65:16: warning: nested namespace definition is a C++17 extension; define each namespace separately [-Wc++17-extensions]
  namespace std::placeholders {
               ^~~~~~~~~~~~~~
                { namespace placeholders
p754.cpp:67:1: error: C++ requires a type specifier for all declarations
see_below_1; 
^
p754.cpp:68:1: error: C++ requires a type specifier for all declarations
see_below_2; 
^
p754.cpp:69:2: error: C++ requires a type specifier for all declarations
 see_below_M;
 ^
p754.cpp:76:8: error: unknown type name 'constexpr'
inline constexpr unspecified _1{};
       ^
p754.cpp:76:1: warning: inline variables are a C++17 extension [-Wc++17-extensions]
inline constexpr unspecified _1{};
^
p754.cpp:76:29: error: expected ';' after top level declarator
inline constexpr unspecified _1{};
                            ^
                            ;
p754.cpp:78:8: error: unknown type name 'unspecified'
extern unspecified _1;
       ^
6 warnings and 14 errors generated.
$ clang++ p754.cpp -std=2b -o p754l -I. -Wall
p754.cpp:40:1: error: expected unqualified-id
static_cast<cv TDi &>(tdi )(std::forward<Uj >(uj )...) 
^
p754.cpp:57:11: error: unknown type name 'unspecified'
constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
          ^
p754.cpp:67:1: error: C++ requires a type specifier for all declarations
see_below_1; 
^
p754.cpp:68:1: error: C++ requires a type specifier for all declarations
see_below_2; 
^
p754.cpp:69:2: error: C++ requires a type specifier for all declarations
 see_below_M;
 ^
p754.cpp:76:18: error: unknown type name 'unspecified'
inline constexpr unspecified _1{};
                 ^
p754.cpp:78:8: error: unknown type name 'unspecified'
extern unspecified _1;
       ^
7 errors generated.

$ g++ p754.cpp -std=03 -o p754g -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from N4910.h:11,
                 from p754.cpp:10:
/usr/local/include/c++/12.1.0/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
   32 | #error This file requires compiler and library support \
      |  ^~~~~
p754.cpp:55:1: warning: identifier 'constexpr' is a keyword in C++11 [-Wc++11-compat]
   55 | constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
      | ^~~~~~~~~
p754.cpp:40:1: error: expected unqualified-id before 'static_cast'
   40 | static_cast<cv TDi &>(tdi )(std::forward<Uj >(uj )...)
      | ^~~~~~~~~~~
p754.cpp:56:33: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   56 | template<class R, class F, class... BoundArgs>
      |                                 ^~~
p754.cpp:57:1: error: 'constexpr' does not name a type
   57 | constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
      | ^~~~~~~~~
p754.cpp:57:1: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p754.cpp:67:1: error: 'see_below_1' does not name a type
   67 | see_below_1;
      | ^~~~~~~~~~~
p754.cpp:68:1: error: 'see_below_2' does not name a type
   68 | see_below_2;
      | ^~~~~~~~~~~
p754.cpp:69:2: error: 'see_below_M' does not name a type
   69 |  see_below_M;
      |  ^~~~~~~~~~~
p754.cpp:76:8: error: 'constexpr' does not name a type
   76 | inline constexpr unspecified _1{};
      |        ^~~~~~~~~
p754.cpp:76:8: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p754.cpp:78:8: error: 'unspecified' does not name a type
   78 | extern unspecified _1;
      |        ^~~~~~~~~~~

$ g++ p754.cpp -std=2b -o p754g -I. -Wall
p754.cpp:40:1: error: expected unqualified-id before 'static_cast'
   40 | static_cast<cv TDi &>(tdi )(std::forward<Uj >(uj )...)
      | ^~~~~~~~~~~
p754.cpp:57:11: error: 'unspecified' does not name a type
   57 | constexpr unspecified bind(F&& f, BoundArgs&&... bound_args);
      |           ^~~~~~~~~~~
p754.cpp:67:1: error: 'see_below_1' does not name a type
   67 | see_below_1;
      | ^~~~~~~~~~~
p754.cpp:68:1: error: 'see_below_2' does not name a type
   68 | see_below_2;
      | ^~~~~~~~~~~
p754.cpp:69:2: error: 'see_below_M' does not name a type
   69 |  see_below_M;
      |  ^~~~~~~~~~~
p754.cpp:76:18: error: 'unspecified' does not name a type
   76 | inline constexpr unspecified _1{};
      |                  ^~~~~~~~~~~
p754.cpp:78:8: error: 'unspecified' does not name a type
   78 | extern unspecified _1;
      |        ^~~~~~~~~~~

```

## 検討事項(agenda)
コンパイルエラーを取るか、コンパイルエラーの理由を解説する。

<!-- リンクエラーの解説をする。clang++とg++の比較。意味のある出力。
コンパイルエラーを取るか、コンパイルエラーの理由を解説する。-->

# 参考資料(reference)


関連する自己参照以外は、こちらの先頭に移転。

C言語（C++)に対する誤解、曲解、無理解、爽快。

https://qiita.com/kaizen_nagoya/items/3f3992c9722c1cee2e3a

#include "N4910.h"

https://qiita.com/kaizen_nagoya/items/163a47cef7d6bb1c33a8

C++N4910資料の改善点

https://qiita.com/kaizen_nagoya/items/fb4ceb5d117a54641af3

dockerにclang

https://qiita.com/kaizen_nagoya/items/8829ffeee397eda50e80

docker gnu(gcc/g++) and llvm(clang/clang++)

https://qiita.com/drafts/059874ea39c4de64c0f7

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


C++N4910:2022 tag follower 300人超えました。ありがとうございます。

https://qiita.com/kaizen_nagoya/items/a63fb96d351ac5c16ff7

astyle 使ってみた

https://qiita.com/kaizen_nagoya/items/3c9a87a781d53a1a23f3

DoCAP（ドゥーキャップ）って何ですか？

https://qiita.com/kaizen_nagoya/items/47e0e6509ab792c43327

小川メソッド　覚え（書きかけ）

https://qiita.com/kaizen_nagoya/items/3593d72eca551742df68

 ＜この記事は個人の過去の経験に基づく個人の感想です。現在所属する組織、業務とは関係がありません。＞

# 文書履歴(document history)
ver. 0.01 初稿 　20220731