22.5.3.4 Assignment [optional.assign] C++N4910:2022 (549) p691a.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
https://cpprefjp.github.io
http://ja.cppreference.com/

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.

# 22.5.3.4 Assignment optional.assignC++N4910:2022 (549) p691a.cpp

## 算譜(source code)

```c++:p691a.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 = "22.5.3.4 Assignment optional.assignC++N4910:2022 (549) p691a.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 <iostream>
#include <cstdio>
#include <cstdlib> 
#include <cstring>
#include <cassert>
#include <coroutine>
#include <vector>
#include <complex>
#include <map>
#include <atomic>
#include <unordered_map>
#include <memory>
#include <typeinfo>

using namespace std;

// Example 1  
constexpr optional<T>& operator=(nullopt_t) noexcept;
// Effects: If *this contains a value, calls val->T::~T() to destroy the contained value; otherwise no effect.
// Postconditions: *this does not contain a value. Returns: *this.
constexpr optional<T>& operator=(const optional& rhs);
// Effects: See Table 57.
// Postconditions: rhs.has_value() == this->has_value().
// Returns: *this.
// Remarks: If any exception is thrown, the result of the expression this->has_value() remains un- changed. If an exception is thrown during the call to T’s copy constructor, no effect. If an exception is thrown during the call to T’s copy assignment, the state of its contained value is as defined by the exception safety guarantee of T’s copy assignment. This operator is defined as deleted unless is_- copy_constructible_v<T> is true and is_copy_assignable_v<T> is true. If is_trivially_copy_- constructible_v<T> && is_trivially_copy_assignable_v<T> && is_trivially_destructible_- v<T> is true, this assignment operator is trivial.
constexpr optional& operator=(optional&& rhs) noexcept(see below);
// Constraints: is_move_constructible_v<T> is true and is_move_assignable_v<T> is true. Effects: See Table 58. The result of the expression rhs.has_value() remains unchanged.
// Postconditions: rhs.has_value() == this->has_value(). Returns: *this.
// Remarks: The exception specification is equivalent to:
  is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
// If any exception is thrown, the result of the expression this->has_value() remains unchanged. If an exception is thrown during the call to T’s move constructor, the state of *rhs.val is determined by the exception safety guarantee of T’s move constructor. If an exception is thrown during the call to T’s move assignment, the state of *val and *rhs.val is determined by the exception safety guarantee of T’s move assignment. If is_trivially_move_constructible_v<T> && is_trivially_move_assignable_v<T> && is_trivially_destructible_v<T> is true, this assignment operator is trivial.
template<class U = T> constexpr optional<T>& operator=(U&& v);
// Constraints: is_same_v<remove_cvref_t<U>, optional> is false, conjunction_v<is_scalar<T>, is_same<T, decay_t<U>>> is false, is_constructible_v<T, U> is true, and is_assignable_v<T&, U> is true.
// Effects: If *this contains a value, assigns std::forward<U>(v) to the contained value; otherwise direct-non-list-initializes the contained value with std::forward<U>(v).
// Postconditions: *this contains a value.
// Returns: *this.
// Remarks: If any exception is thrown, the result of the expression this->has_value() remains un- changed. If an exception is thrown during the call to T’s constructor, the state of v is determined by the exception safety guarantee of T’s constructor. If an exception is thrown during the call to T’s assignment, the state of *val and v is determined by the exception safety guarantee of T’s assignment.
template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
// Constraints:
// — is_constructible_v<T, const U&> is true,
// — is_assignable_v<T&, const U&> is true,
// — is_constructible_v<T, optional<U>&> is false,
// — is_constructible_v<T, optional<U>&&> is false,
// — is_constructible_v<T, const optional<U>&> is false, 
// — is_constructible_v<T, const optional<U>&&> is false, 
// — is_convertible_v<optional<U>&, T> is false,
// — is_convertible_v<optional<U>&&, T> is false,
// — is_convertible_v<const optional<U>&, T> is false,
// — is_convertible_v<const optional<U>&&, T> is false,
// — is_assignable_v<T&, optional<U>&> is false,
// — is_assignable_v<T&, optional<U>&&> is false,
// — is_assignable_v<T&, const optional<U>&> is false, and 
// — is_assignable_v<T&, const optional<U>&&> is false.
// Effects: See Table 59.
// Postconditions: rhs.has_value() == this->has_value().
// Returns: *this.
// Remarks: If any exception is thrown, the result of the expression this->has_value() remains un- changed. If an exception is thrown during the call to T’s constructor, the state of *rhs.val is determined by the exception safety guarantee of T’s constructor. If an exception is thrown during the call to T’s assignment, the state of *val and *rhs.val is determined by the exception safety guarantee of T’s assignment.
template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
// Constraints:
// — is_constructible_v<T, U> is true,
// — is_assignable_v<T&, U> is true,
// — is_constructible_v<T, optional<U>&> is false,
// — is_constructible_v<T, optional<U>&&> is false,
// — is_constructible_v<T, const optional<U>&> is false, 
// — is_constructible_v<T, const optional<U>&&> is false, 
// — is_convertible_v<optional<U>&, T> is false,
// — is_convertible_v<optional<U>&&, T> is false,
// — is_convertible_v<const optional<U>&, T> is false,
// — is_convertible_v<const optional<U>&&, T> is false,
// — is_assignable_v<T&, optional<U>&> is false,
// — is_assignable_v<T&, optional<U>&&> is false,
// — is_assignable_v<T&, const optional<U>&> is false, and 
// — is_assignable_v<T&, const optional<U>&&> is false.
// Effects: See Table 60. The result of the expression rhs.has_value() remains unchanged.
// Postconditions: rhs.has_value() == this->has_value().
// Returns: *this.
// Remarks: If any exception is thrown, the result of the expression this->has_value() remains un- changed. If an exception is thrown during the call to T’s constructor, the state of *rhs.val is determined by the exception safety guarantee of T’s constructor. If an exception is thrown during the call to T’s assignment, the state of *val and *rhs.val is determined by the exception safety guarantee of T’s assignment.
template<class... Args> constexpr T& emplace(Args&&... args);
// Mandates: is_constructible_v<T, Args...> is true.
// Effects: Calls *this = nullopt. Then direct-non-list-initializes the contained value with std::forward
<Args>(args)....
// Postconditions: *this contains a value.
// Returns: A reference to the new contained value.
// Throws: Any exception thrown by the selected constructor of T.
// Remarks: If an exception is thrown during the call to T’s constructor, *this does not contain a value, and the previous *val (if any) has been destroyed.
template<class U, class... Args> constexpr T& emplace(initializer_list<U> il, Args&&... args);
// Constraints: is_constructible_v<T, initializer_list<U>&, Args...> is true.
// Effects: Calls *this = nullopt. Then direct-non-list-initializes the contained value with il, std::
forward<Args>(args)....
// Postconditions: *this contains a value.
// Returns: A reference to the new contained value.
// Throws: Any exception thrown by the selected constructor of T.
// Remarks: If an exception is thrown during the call to T’s constructor, *this does not contain a value, and the previous *val (if any) has been destroyed.
int main(){
  cout  <<  n4910 << endl;
  return EXIT_SUCCESS;
}
```

## 編纂・実行結果(compile and go)

```ubuntu:bash
$ clang++ p691a.cpp -std=03 -o p691al -I. -Wall
In file included from p691a.cpp:19:
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 \
 ^
p691a.cpp:27:1: error: unknown type name 'constexpr'
constexpr optional<T>& operator=(nullopt_t) noexcept;
^
p691a.cpp:27:20: error: use of undeclared identifier 'T'
constexpr optional<T>& operator=(nullopt_t) noexcept;
                   ^
p691a.cpp:30:1: error: unknown type name 'constexpr'
constexpr optional<T>& operator=(const optional& rhs);
^
p691a.cpp:30:20: error: use of undeclared identifier 'T'
constexpr optional<T>& operator=(const optional& rhs);
                   ^
p691a.cpp:35:1: error: unknown type name 'constexpr'
constexpr optional& operator=(optional&& rhs) noexcept(see below);
^
p691a.cpp:35:19: error: expected ';' after top level declarator
constexpr optional& operator=(optional&& rhs) noexcept(see below);
                  ^
                  ;
p691a.cpp:39:32: error: use of undeclared identifier 'T'
  is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
                               ^
p691a.cpp:39:35: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
  is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
                                  ^
p691a.cpp:39:70: error: use of undeclared identifier 'T'
  is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
                                                                     ^
p691a.cpp:47:19: error: unknown type name 'constexpr'
template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
                  ^
p691a.cpp:47:29: warning: variable templates are a C++14 extension [-Wc++14-extensions]
template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
                            ^
p691a.cpp:47:37: error: expected ';' at end of declaration
template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
                                    ^
                                    ;
p691a.cpp:47:37: error: expected unqualified-id
p691a.cpp:67:19: error: unknown type name 'constexpr'
template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
                  ^
p691a.cpp:67:29: warning: variable templates are a C++14 extension [-Wc++14-extensions]
template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
                            ^
p691a.cpp:67:37: error: expected ';' at end of declaration
template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
                                    ^
                                    ;
p691a.cpp:67:37: error: expected unqualified-id
p691a.cpp:87:15: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class... Args> constexpr T& emplace(Args&&... args);
              ^
p691a.cpp:87:25: error: unknown type name 'constexpr'
template<class... Args> constexpr T& emplace(Args&&... args);
                        ^
p691a.cpp:87:35: warning: variable templates are a C++14 extension [-Wc++14-extensions]
template<class... Args> constexpr T& emplace(Args&&... args);
                                  ^
p691a.cpp:87:36: error: expected ';' at end of declaration
template<class... Args> constexpr T& emplace(Args&&... args);
                                   ^
                                   ;
p691a.cpp:87:46: error: unknown type name 'Args'
template<class... Args> constexpr T& emplace(Args&&... args);
                                             ^
p691a.cpp:87:50: warning: rvalue references are a C++11 extension [-Wc++11-extensions]
template<class... Args> constexpr T& emplace(Args&&... args);
                                                 ^
p691a.cpp:87:52: error: type 'int &&' of function parameter pack does not contain any unexpanded parameter packs
template<class... Args> constexpr T& emplace(Args&&... args);
                                             ~~~~~~^~~~~~~~
fatal error: too many errors emitted, stopping now [-ferror-limit=]
6 warnings and 20 errors generated.
$ clang++ p691a.cpp -std=2b -o p691al -I. -Wall
p691a.cpp:27:20: error: use of undeclared identifier 'T'
constexpr optional<T>& operator=(nullopt_t) noexcept;
                   ^
p691a.cpp:30:20: error: use of undeclared identifier 'T'
constexpr optional<T>& operator=(const optional& rhs);
                   ^
p691a.cpp:30:40: error: use of class template 'optional' requires template arguments; argument deduction not allowed in function prototype
constexpr optional<T>& operator=(const optional& rhs);
                                       ^~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/optional:659:11: note: template is declared here
    class optional
          ^
p691a.cpp:35:31: error: use of class template 'optional' requires template arguments; argument deduction not allowed in function prototype
constexpr optional& operator=(optional&& rhs) noexcept(see below);
                              ^~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/optional:659:11: note: template is declared here
    class optional
          ^
p691a.cpp:35:56: error: use of undeclared identifier 'see'
constexpr optional& operator=(optional&& rhs) noexcept(see below);
                                                       ^
p691a.cpp:35:60: error: expected ')'
constexpr optional& operator=(optional&& rhs) noexcept(see below);
                                                           ^
p691a.cpp:35:55: note: to match this '('
constexpr optional& operator=(optional&& rhs) noexcept(see below);
                                                      ^
p691a.cpp:35:11: error: use of class template 'optional' requires template arguments; argument deduction not allowed in function return type
constexpr optional& operator=(optional&& rhs) noexcept(see below);
          ^~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/optional:659:11: note: template is declared here
    class optional
          ^
p691a.cpp:39:32: error: use of undeclared identifier 'T'
  is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
                               ^
p691a.cpp:47:38: error: use of undeclared identifier 'T'
template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
                                     ^
p691a.cpp:67:38: error: use of undeclared identifier 'T'
template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
                                     ^
p691a.cpp:87:35: error: unknown type name 'T'
template<class... Args> constexpr T& emplace(Args&&... args);
                                  ^
p691a.cpp:90:1: error: expected unqualified-id
<Args>(args)....
^
p691a.cpp:98:9: error: use of undeclared identifier 'Args'
forward<Args>(args)....
        ^
p691a.cpp:98:15: error: use of undeclared identifier 'args'; did you mean 'arg'?
forward<Args>(args)....
              ^~~~
              arg
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/complex:652:5: note: 'arg' declared here
    arg(const complex<_Tp>& __z) { return __complex_arg(__z.__rep()); }
    ^
14 errors generated.

$ g++ p691a.cpp -std=03 -o p691ag -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from p691a.cpp:19:
/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 \
      |  ^~~~~
p691a.cpp:27:1: warning: identifier 'constexpr' is a keyword in C++11 [-Wc++11-compat]
   27 | constexpr optional<T>& operator=(nullopt_t) noexcept;
      | ^~~~~~~~~
p691a.cpp:27:45: warning: identifier 'noexcept' is a keyword in C++11 [-Wc++11-compat]
   27 | constexpr optional<T>& operator=(nullopt_t) noexcept;
      |                                             ^~~~~~~~
p691a.cpp:27:1: error: 'constexpr' does not name a type
   27 | constexpr optional<T>& operator=(nullopt_t) noexcept;
      | ^~~~~~~~~
p691a.cpp:27:1: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p691a.cpp:30:1: error: 'constexpr' does not name a type
   30 | constexpr optional<T>& operator=(const optional& rhs);
      | ^~~~~~~~~
p691a.cpp:30:1: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p691a.cpp:35:1: error: 'constexpr' does not name a type
   35 | constexpr optional& operator=(optional&& rhs) noexcept(see below);
      | ^~~~~~~~~
p691a.cpp:35:1: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p691a.cpp:39:3: error: 'is_nothrow_move_assignable_v' does not name a type
   39 |   is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
p691a.cpp:47:19: error: 'constexpr' does not name a type
   47 | template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
      |                   ^~~~~~~~~
p691a.cpp:47:19: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p691a.cpp:67:19: error: 'constexpr' does not name a type
   67 | template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
      |                   ^~~~~~~~~
p691a.cpp:67:19: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p691a.cpp:87:15: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   87 | template<class... Args> constexpr T& emplace(Args&&... args);
      |               ^~~
p691a.cpp:87:25: error: 'constexpr' does not name a type
   87 | template<class... Args> constexpr T& emplace(Args&&... args);
      |                         ^~~~~~~~~
p691a.cpp:87:25: note: C++11 'constexpr' only available with '-std=c++11' or '-std=gnu++11'
p691a.cpp:90:1: error: expected unqualified-id before '<' token
   90 | <Args>(args)....
      | ^
p691a.cpp:98:1: error: 'forward' does not name a type
   98 | forward<Args>(args)....
      | ^~~~~~~

$ g++ p691a.cpp -std=2b -o p691ag -I. -Wall
p691a.cpp:27:20: error: 'T' was not declared in this scope
   27 | constexpr optional<T>& operator=(nullopt_t) noexcept;
      |                    ^
p691a.cpp:27:20: error: 'T' was not declared in this scope
p691a.cpp:27:20: error: 'T' was not declared in this scope
p691a.cpp:27:20: error: 'T' was not declared in this scope
p691a.cpp:27:20: error: 'T' was not declared in this scope
p691a.cpp:27:20: error: 'T' was not declared in this scope
p691a.cpp:27:20: error: 'T' was not declared in this scope
p691a.cpp:27:20: error: 'T' was not declared in this scope
p691a.cpp:27:11: error: 'optional' does not name a type
   27 | constexpr optional<T>& operator=(nullopt_t) noexcept;
      |           ^~~~~~~~
p691a.cpp:30:20: error: 'T' was not declared in this scope
   30 | constexpr optional<T>& operator=(const optional& rhs);
      |                    ^
p691a.cpp:30:20: error: 'T' was not declared in this scope
p691a.cpp:30:20: error: 'T' was not declared in this scope
p691a.cpp:30:20: error: 'T' was not declared in this scope
p691a.cpp:30:20: error: 'T' was not declared in this scope
p691a.cpp:30:20: error: 'T' was not declared in this scope
p691a.cpp:30:20: error: 'T' was not declared in this scope
p691a.cpp:30:20: error: 'T' was not declared in this scope
p691a.cpp:30:11: error: 'optional' does not name a type
   30 | constexpr optional<T>& operator=(const optional& rhs);
      |           ^~~~~~~~
p691a.cpp:35:11: error: 'optional' does not name a type
   35 | constexpr optional& operator=(optional&& rhs) noexcept(see below);
      |           ^~~~~~~~
p691a.cpp:39:32: error: 'T' was not declared in this scope
   39 |   is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
      |                                ^
p691a.cpp:39:3: error: 'is_nothrow_move_assignable_v<<expression error> >' does not name a type
   39 |   is_nothrow_move_assignable_v<T> && is_nothrow_move_constructible_v<T>
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
p691a.cpp:47:38: error: 'T' was not declared in this scope
   47 | template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
      |                                      ^
p691a.cpp:47:38: error: 'T' was not declared in this scope
p691a.cpp:47:38: error: 'T' was not declared in this scope
p691a.cpp:47:38: error: 'T' was not declared in this scope
p691a.cpp:47:38: error: 'T' was not declared in this scope
p691a.cpp:47:38: error: 'T' was not declared in this scope
p691a.cpp:47:38: error: 'T' was not declared in this scope
p691a.cpp:47:38: error: 'T' was not declared in this scope
p691a.cpp:47:29: error: 'optional' does not name a type
   47 | template<class U> constexpr optional<T>& operator=(const optional<U>& rhs);
      |                             ^~~~~~~~
p691a.cpp:67:38: error: 'T' was not declared in this scope
   67 | template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
      |                                      ^
p691a.cpp:67:38: error: 'T' was not declared in this scope
p691a.cpp:67:38: error: 'T' was not declared in this scope
p691a.cpp:67:38: error: 'T' was not declared in this scope
p691a.cpp:67:38: error: 'T' was not declared in this scope
p691a.cpp:67:38: error: 'T' was not declared in this scope
p691a.cpp:67:38: error: 'T' was not declared in this scope
p691a.cpp:67:38: error: 'T' was not declared in this scope
p691a.cpp:67:29: error: 'optional' does not name a type
   67 | template<class U> constexpr optional<T>& operator=(optional<U>&& rhs);
      |                             ^~~~~~~~
p691a.cpp:87:35: error: 'T' does not name a type
   87 | template<class... Args> constexpr T& emplace(Args&&... args);
      |                                   ^
p691a.cpp:90:1: error: expected unqualified-id before '<' token
   90 | <Args>(args)....
      | ^
p691a.cpp:98:9: error: 'Args' was not declared in this scope
   98 | forward<Args>(args)....
      |         ^~~~
p691a.cpp:98:1: error: specializing member '::forward<<expression error> >' requires 'template<>' syntax
   98 | forward<Args>(args)....
      | ^~~~~~~~~~~~~

```

## 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)

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


typedef は C++11 ではオワコン

https://qiita.com/Linda_pp/items/44a67c64c14cba00eef1

C99からC++14を駆け抜けるC++講座

https://qiita.com/yumetodo/items/e49a673afd9a3ecb81a8


@kazuo_reve 私が効果を確認した「小川メソッド」

https://qiita.com/kazuo_reve/items/a3ea1d9171deeccc04da

## 自己参照(self reference)

ocker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 200人超えました。ありがとうございます。

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

C++N4910:2022 tag follower 200人超えました。ありがとうございます。

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

コピペコンパイルエラーあるある

https://qiita.com/kaizen_nagoya/items/29c832de9d762aed2761

C++ Error Message Collection(1)does not name a type, 11 articles

https://qiita.com/kaizen_nagoya/items/acb9f1a9b5aad6df06bd

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

Compare the contents of C++N4910:2022, C++N4741:2018 and C++N4606:2015

https://qiita.com/kaizen_nagoya/items/483246d40f98abff7ded

C++ sample list

https://qiita.com/kaizen_nagoya/items/54ad75b73825b7c04f86

clang++, g++コンパイルエラー方針の違いの例

https://qiita.com/kaizen_nagoya/items/ea6e5009fe126d270a82

astyle 使ってみた

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

C++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

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 　20220725