22.10.9 Concept-constrained comparisons [range.cmp] C++N4910:2022 (619) p748.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.

#  22.10.9 Concept-constrained comparisons [range.cmp] C++N4910:2022 (619) p748.cpp

## 算譜(source code)

```c++:p748.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 = " 22.10.9 Concept-constrained comparisons [range.cmp] C++N4910:2022 (619) p748.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;

// 
struct ranges::equal_to {
    template<class T, class U>
      constexpr bool operator()(T&& t, U&& u) const;
using is_transparent = unspecified; };
template<class T, class U>
  constexpr bool operator()(T&& t, U&& u) const;
// Constraints: T and U satisfy equality_comparable_with.
// Preconditions: If the expression std::forward<T>(t) == std::forward<U>(u) results in a call to a built-in operator == comparing pointers of type P, the conversion sequences from both T and U to P are equality-preserving (18.2); otherwise, T and U model equality_comparable_with.
// Effects: — If the expression std::forward<T>(t) == std::forward<U>(u) results in a call to a built-in operator == comparing pointers: returns false if either (the converted value of) t precedes u or u precedes t in the implementation-defined strict total order over pointers (3.27) and otherwise true.
// — Otherwise, equivalent to: return std::forward<T>(t) == std::forward<U>(u);
struct ranges::not_equal_to {
  template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
using is_transparent = unspecified; };
template<class T, class U>
  constexpr bool operator()(T&& t, U&& u) const;
// Constraints: T and U satisfy equality_comparable_with. Effects: Equivalent to:
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
struct ranges::greater {
  template<class T, class U>
  constexpr bool operator()(T&& t, U&& u) const;
using is_transparent = unspecified; };
// Constraints: T and U satisfy totally_ordered_with.
// Preconditions: If the expression std::forward<T>(t) < std::forward<U>(u) results in a call to a built-in operator < comparing pointers of type P, the conversion sequences from both T and U to P are equality-preserving (18.2); otherwise, T and U model totally_ordered_with. For any expressions ET and EU such that decltype((ET)) is T and decltype((EU)) is U, exactly one of ranges::less{}(ET, EU), ranges::less{}(EU, ET), or ranges::equal_to{}(ET, EU) is true.
// Effects:— If the expression std::forward<T>(t) < std::forward<U>(u) results in a call to a built-in operator < comparing pointers: returns true if (the converted value of) t precedes u in the implementation-defined strict total order over pointers (3.27) and otherwise false.
// - Otherwise, equivalent to: return std::forward<T>(t) < std::forward<U>(u);
// Constraints: T and U satisfy totally_ordered_with. Effects: Equivalent to:
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
   template<class T, class U>
     constexpr bool operator()(T&& t, U&& u) const;
// Constraints: T and U satisfy totally_ordered_with. Effects: Equivalent to:
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
struct ranges::less {
  template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
using is_transparent = unspecified; };
template<class T, class U>
  constexpr bool operator()(T&& t, U&& u) const;
struct ranges::greater_equal {
  template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
using is_transparent = unspecified; };
template<class T, class U>
  constexpr bool operator()(T&& t, U&& u) const;
// Constraints: T and U satisfy totally_ordered_with. Effects: Equivalent to:
  return !ranges::less{}(std::forward<T>(t), std::forward<U>(u));
struct ranges::less_equal {
  template<class T, class U>
    constexpr bool operator()(T&& t, U&& u) const;
using is_transparent = unspecified; };
template<class T, class U>
  constexpr bool operator()(T&& t, U&& u) const;
int main(){
  cout  <<  n4910 << endl;
  return EXIT_SUCCESS;
}
```

## 編纂・実行結果(compile and go)

```ubuntu:bash
$ clang++ p748.cpp -std=03 -o p748l -I. -Wall
In file included from p748.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 \
 ^
p748.cpp:15:8: error: use of undeclared identifier 'ranges'
struct ranges::equal_to {
       ^
p748.cpp:20:3: error: unknown type name 'constexpr'
  constexpr bool operator()(T&& t, U&& u) const;
  ^
p748.cpp:20:30: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
  constexpr bool operator()(T&& t, U&& u) const;
                             ^
p748.cpp:20:37: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
  constexpr bool operator()(T&& t, U&& u) const;
                                    ^
p748.cpp:20:43: error: non-member function cannot have 'const' qualifier
  constexpr bool operator()(T&& t, U&& u) const;
                                          ^~~~~
p748.cpp:25:8: error: use of undeclared identifier 'ranges'
struct ranges::not_equal_to {
       ^
p748.cpp:30:3: error: unknown type name 'constexpr'
  constexpr bool operator()(T&& t, U&& u) const;
  ^
p748.cpp:30:30: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
  constexpr bool operator()(T&& t, U&& u) const;
                             ^
p748.cpp:30:37: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
  constexpr bool operator()(T&& t, U&& u) const;
                                    ^
p748.cpp:30:43: error: non-member function cannot have 'const' qualifier
  constexpr bool operator()(T&& t, U&& u) const;
                                          ^~~~~
p748.cpp:32:6: error: expected unqualified-id
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
     ^
p748.cpp:32:45: error: expected ')'
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                                            ^
p748.cpp:32:32: note: to match this '('
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                               ^
p748.cpp:32:38: error: C++ requires a type specifier for all declarations
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                                     ^
p748.cpp:32:38: error: no member named 'forward' in namespace 'std'
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                                ~~~~~^
p748.cpp:33:8: error: use of undeclared identifier 'ranges'
struct ranges::greater {
       ^
p748.cpp:42:8: error: expected unqualified-id
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
       ^
p748.cpp:42:43: error: expected ')'
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                          ^
p748.cpp:42:30: note: to match this '('
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                             ^
p748.cpp:42:36: error: C++ requires a type specifier for all declarations
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                   ^
p748.cpp:44:6: error: unknown type name 'constexpr'
     constexpr bool operator()(T&& t, U&& u) const;
     ^
p748.cpp:44:33: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
     constexpr bool operator()(T&& t, U&& u) const;
                                ^
p748.cpp:44:40: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
     constexpr bool operator()(T&& t, U&& u) const;
                                       ^
p748.cpp:44:46: error: non-member function cannot have 'const' qualifier
     constexpr bool operator()(T&& t, U&& u) const;
                                             ^~~~~
p748.cpp:46:6: error: expected unqualified-id
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
     ^
p748.cpp:46:40: error: expected ')'
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                       ^
p748.cpp:46:27: note: to match this '('
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                          ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
6 warnings and 20 errors generated.
$ clang++ p748.cpp -std=2b -o p748l -I. -Wall
p748.cpp:15:16: error: redefinition of 'equal_to'
struct ranges::equal_to {
               ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/range_cmp.h:92:10: note: previous definition is here
  struct equal_to
         ^
p748.cpp:20:43: error: non-member function cannot have 'const' qualifier
  constexpr bool operator()(T&& t, U&& u) const;
                                          ^~~~~
p748.cpp:20:18: error: overloaded 'operator()' must be a non-static member function
  constexpr bool operator()(T&& t, U&& u) const;
                 ^
p748.cpp:25:16: error: redefinition of 'not_equal_to'
struct ranges::not_equal_to {
               ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/range_cmp.h:106:10: note: previous definition is here
  struct not_equal_to
         ^
p748.cpp:30:43: error: non-member function cannot have 'const' qualifier
  constexpr bool operator()(T&& t, U&& u) const;
                                          ^~~~~
p748.cpp:32:6: error: expected unqualified-id
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
     ^
p748.cpp:32:46: error: use of undeclared identifier 'T'
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                                             ^
p748.cpp:32:49: error: unknown type name 't'
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                                                ^
p748.cpp:32:51: error: expected ')'
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                                                  ^
p748.cpp:32:32: note: to match this '('
     return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
                               ^
p748.cpp:33:16: error: redefinition of 'greater'
struct ranges::greater {
               ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/range_cmp.h:149:10: note: previous definition is here
  struct greater
         ^
p748.cpp:42:8: error: expected unqualified-id
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
       ^
p748.cpp:42:44: error: use of undeclared identifier 'U'
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                           ^
p748.cpp:42:47: error: unknown type name 'u'
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                              ^
p748.cpp:42:49: error: expected ')'
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                                ^
p748.cpp:42:30: note: to match this '('
       return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                             ^
p748.cpp:44:46: error: non-member function cannot have 'const' qualifier
     constexpr bool operator()(T&& t, U&& u) const;
                                             ^~~~~
p748.cpp:46:6: error: expected unqualified-id
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
     ^
p748.cpp:46:41: error: use of undeclared identifier 'U'
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                        ^
p748.cpp:46:44: error: unknown type name 'u'
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                           ^
p748.cpp:46:46: error: expected ')'
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                                             ^
p748.cpp:46:27: note: to match this '('
     return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
                          ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.

$ g++ p748.cpp -std=03 -o p748g -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from N4910.h:11,
                 from p748.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 \
      |  ^~~~~
p748.cpp:17:7: warning: identifier 'constexpr' is a keyword in C++11 [-Wc++11-compat]
   17 |       constexpr bool operator()(T&& t, U&& u) const;
      |       ^~~~~~~~~
p748.cpp:15:8: error: 'ranges' has not been declared
   15 | struct ranges::equal_to {
      |        ^~~~~~
p748.cpp:15:25: error: expected unqualified-id before '{' token
   15 | struct ranges::equal_to {
      |                         ^
p748.cpp:20:3: error: 'constexpr' does not name a type
   20 |   constexpr bool operator()(T&& t, U&& u) const;
      |   ^~~~~~~~~
p748.cpp:20:3: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p748.cpp:25:8: error: 'ranges' has not been declared
   25 | struct ranges::not_equal_to {
      |        ^~~~~~
p748.cpp:25:29: error: expected unqualified-id before '{' token
   25 | struct ranges::not_equal_to {
      |                             ^
p748.cpp:30:3: error: 'constexpr' does not name a type
   30 |   constexpr bool operator()(T&& t, U&& u) const;
      |   ^~~~~~~~~
p748.cpp:30:3: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p748.cpp:32:6: error: expected unqualified-id before 'return'
   32 |      return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
      |      ^~~~~~
p748.cpp:32:45: error: expected ')' before '<' token
   32 |      return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
      |                                ~            ^
      |                                             )
p748.cpp:33:8: error: 'ranges' has not been declared
   33 | struct ranges::greater {
      |        ^~~~~~
p748.cpp:33:24: error: expected unqualified-id before '{' token
   33 | struct ranges::greater {
      |                        ^
p748.cpp:42:8: error: expected unqualified-id before 'return'
   42 |        return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |        ^~~~~~
p748.cpp:42:43: error: expected ')' before '<' token
   42 |        return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |                              ~            ^
      |                                           )
p748.cpp:44:6: error: 'constexpr' does not name a type
   44 |      constexpr bool operator()(T&& t, U&& u) const;
      |      ^~~~~~~~~
p748.cpp:44:6: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p748.cpp:46:6: error: expected unqualified-id before 'return'
   46 |      return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |      ^~~~~~
p748.cpp:46:40: error: expected ')' before '<' token
   46 |      return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |                           ~            ^
      |                                        )
p748.cpp:47:8: error: 'ranges' has not been declared
   47 | struct ranges::less {
      |        ^~~~~~
p748.cpp:47:21: error: expected unqualified-id before '{' token
   47 | struct ranges::less {
      |                     ^
p748.cpp:52:3: error: 'constexpr' does not name a type
   52 |   constexpr bool operator()(T&& t, U&& u) const;
      |   ^~~~~~~~~
p748.cpp:52:3: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p748.cpp:53:8: error: 'ranges' has not been declared
   53 | struct ranges::greater_equal {
      |        ^~~~~~
p748.cpp:53:30: error: expected unqualified-id before '{' token
   53 | struct ranges::greater_equal {
      |                              ^
p748.cpp:58:3: error: 'constexpr' does not name a type
   58 |   constexpr bool operator()(T&& t, U&& u) const;
      |   ^~~~~~~~~
p748.cpp:58:3: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p748.cpp:60:3: error: expected unqualified-id before 'return'
   60 |   return !ranges::less{}(std::forward<T>(t), std::forward<U>(u));
      |   ^~~~~~
p748.cpp:60:38: error: expected ')' before '<' token
   60 |   return !ranges::less{}(std::forward<T>(t), std::forward<U>(u));
      |                         ~            ^
      |                                      )
p748.cpp:61:8: error: 'ranges' has not been declared
   61 | struct ranges::less_equal {
      |        ^~~~~~
p748.cpp:61:27: error: expected unqualified-id before '{' token
   61 | struct ranges::less_equal {
      |                           ^
p748.cpp:66:3: error: 'constexpr' does not name a type
   66 |   constexpr bool operator()(T&& t, U&& u) const;
      |   ^~~~~~~~~
p748.cpp:66:3: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'

$ g++ p748.cpp -std=2b -o p748g -I. -Wall
p748.cpp:15:16: error: redefinition of 'struct std::ranges::equal_to'
   15 | struct ranges::equal_to {
      |                ^~~~~~~~
In file included from /usr/local/include/c++/12.1.0/bits/iterator_concepts.h:37,
                 from /usr/local/include/c++/12.1.0/bits/stl_iterator_base_types.h:71,
                 from /usr/local/include/c++/12.1.0/bits/stl_construct.h:61,
                 from /usr/local/include/c++/12.1.0/bits/char_traits.h:46,
                 from /usr/local/include/c++/12.1.0/ios:40,
                 from /usr/local/include/c++/12.1.0/ostream:38,
                 from /usr/local/include/c++/12.1.0/iostream:39,
                 from N4910.h:2,
                 from p748.cpp:10:
/usr/local/include/c++/12.1.0/bits/ranges_cmp.h:86:10: note: previous definition of 'struct std::ranges::equal_to'
   86 |   struct equal_to
      |          ^~~~~~~~
p748.cpp:20:43: error: non-member function 'constexpr bool operator()(T&&, U&&)' cannot have cv-qualifier
   20 |   constexpr bool operator()(T&& t, U&& u) const;
      |                                           ^~~~~
p748.cpp:20:18: error: 'constexpr bool operator()(T&&, U&&)' must be a non-static member function
   20 |   constexpr bool operator()(T&& t, U&& u) const;
      |                  ^~~~~~~~
p748.cpp:25:16: error: redefinition of 'struct std::ranges::not_equal_to'
   25 | struct ranges::not_equal_to {
      |                ^~~~~~~~~~~~
/usr/local/include/c++/12.1.0/bits/ranges_cmp.h:99:10: note: previous definition of 'struct std::ranges::not_equal_to'
   99 |   struct not_equal_to
      |          ^~~~~~~~~~~~
p748.cpp:30:43: error: non-member function 'constexpr bool operator()(T&&, U&&)' cannot have cv-qualifier
   30 |   constexpr bool operator()(T&& t, U&& u) const;
      |                                           ^~~~~
p748.cpp:30:18: error: 'constexpr bool operator()(T&&, U&&)' must be a non-static member function
   30 |   constexpr bool operator()(T&& t, U&& u) const;
      |                  ^~~~~~~~
p748.cpp:32:6: error: expected unqualified-id before 'return'
   32 |      return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
      |      ^~~~~~
p748.cpp:32:46: error: 'T' was not declared in this scope
   32 |      return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
      |                                              ^
p748.cpp:32:48: error: expected ')' before '(' token
   32 |      return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));
      |                                ~               ^
      |                                                )
p748.cpp:33:16: error: redefinition of 'struct std::ranges::greater'
   33 | struct ranges::greater {
      |                ^~~~~~~
/usr/local/include/c++/12.1.0/bits/ranges_cmp.h:139:10: note: previous definition of 'struct std::ranges::greater'
  139 |   struct greater
      |          ^~~~~~~
p748.cpp:42:8: error: expected unqualified-id before 'return'
   42 |        return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |        ^~~~~~
p748.cpp:42:44: error: 'U' was not declared in this scope
   42 |        return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |                                            ^
p748.cpp:42:46: error: expected ')' before '(' token
   42 |        return !ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |                              ~               ^
      |                                              )
p748.cpp:44:46: error: non-member function 'constexpr bool operator()(T&&, U&&)' cannot have cv-qualifier
   44 |      constexpr bool operator()(T&& t, U&& u) const;
      |                                              ^~~~~
p748.cpp:44:21: error: 'constexpr bool operator()(T&&, U&&)' must be a non-static member function
   44 |      constexpr bool operator()(T&& t, U&& u) const;
      |                     ^~~~~~~~
p748.cpp:46:6: error: expected unqualified-id before 'return'
   46 |      return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |      ^~~~~~
p748.cpp:46:41: error: 'U' was not declared in this scope
   46 |      return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |                                         ^
p748.cpp:46:43: error: expected ')' before '(' token
   46 |      return ranges::less{}(std::forward<U>(u), std::forward<T>(t));
      |                           ~               ^
      |                                           )
p748.cpp:47:16: error: redefinition of 'struct std::ranges::less'
   47 | struct ranges::less {
      |                ^~~~
/usr/local/include/c++/12.1.0/bits/ranges_cmp.h:112:10: note: previous definition of 'struct std::ranges::less'
  112 |   struct less
      |          ^~~~
p748.cpp:52:43: error: non-member function 'constexpr bool operator()(T&&, U&&)' cannot have cv-qualifier
   52 |   constexpr bool operator()(T&& t, U&& u) const;
      |                                           ^~~~~
p748.cpp:52:18: error: 'constexpr bool operator()(T&&, U&&)' must be a non-static member function
   52 |   constexpr bool operator()(T&& t, U&& u) const;
      |                  ^~~~~~~~
p748.cpp:53:16: error: redefinition of 'struct std::ranges::greater_equal'
   53 | struct ranges::greater_equal {
      |                ^~~~~~~~~~~~~
/usr/local/include/c++/12.1.0/bits/ranges_cmp.h:152:10: note: previous definition of 'struct std::ranges::greater_equal'
  152 |   struct greater_equal
      |          ^~~~~~~~~~~~~
p748.cpp:58:43: error: non-member function 'constexpr bool operator()(T&&, U&&)' cannot have cv-qualifier
   58 |   constexpr bool operator()(T&& t, U&& u) const;
      |                                           ^~~~~
p748.cpp:58:18: error: 'constexpr bool operator()(T&&, U&&)' must be a non-static member function
   58 |   constexpr bool operator()(T&& t, U&& u) const;
      |                  ^~~~~~~~
p748.cpp:60:3: error: expected unqualified-id before 'return'
   60 |   return !ranges::less{}(std::forward<T>(t), std::forward<U>(u));
      |   ^~~~~~
p748.cpp:60:39: error: 'T' was not declared in this scope
   60 |   return !ranges::less{}(std::forward<T>(t), std::forward<U>(u));
      |                                       ^
p748.cpp:60:41: error: expected ')' before '(' token
   60 |   return !ranges::less{}(std::forward<T>(t), std::forward<U>(u));
      |                         ~               ^
      |                                         )
p748.cpp:61:16: error: redefinition of 'struct std::ranges::less_equal'
   61 | struct ranges::less_equal {
      |                ^~~~~~~~~~
/usr/local/include/c++/12.1.0/bits/ranges_cmp.h:165:10: note: previous definition of 'struct std::ranges::less_equal'
  165 |   struct less_equal
      |          ^~~~~~~~~~
p748.cpp:66:43: error: non-member function 'constexpr bool operator()(T&&, U&&)' cannot have cv-qualifier
   66 |   constexpr bool operator()(T&& t, U&& u) const;
      |                                           ^~~~~
p748.cpp:66:18: error: 'constexpr bool operator()(T&&, U&&)' must be a non-static member function
   66 |   constexpr bool operator()(T&& t, U&& u) const;
      |                  ^~~~~~~~
```

## 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