10.7 Reachability [module.reach] C++N4910:2022 (136) p256.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.

# 10.7 Reachability [module.reach] C++N4910:2022 (136) p256.cpp

## 算譜(source code)

```c++:p256.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 = "10.7 Reachability [module.reach] C++N4910:2022 (136) p256.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>

using namespace std;

// Example 1  
// Translation unit #1:
       export module M:A;
       export struct B;
// Translation unit #2:
module M:B;
  struct B {
    operator int();
};
// Translation unit #3:
  module M:C;
  import :A;
  B b1;
// Translation unit #4:
  export module M;
  export import :A;
  import :B;
  B b2;
  export void f(B b = B());
// Translation unit #5:
  module X;
  import M;
  B b3;
  void g() { f(); }
// error: no reachable definition of struct B
// error: no reachable definition of struct B // error: no reachable definition of struct B
// [Example 2: Translation unit #1:
  export module A;
  struct X {};
  export using Y = X;
// Translation unit #2:
  module B;
  import A;
  Y y;
  X x;
// OK, definition of X is reachable
// error: X not visible to unqualified lookup
int main(){
  cout  <<  n4910 << endl;
  return EXIT_SUCCESS;
}
```

## Script

```bash:clgc.sh
#!/bin/sh
rm $1l
rm $1g
echo "$ clang++ $1.cpp -std=03 -o $1l -I. -Wall" 
clang++ $1.cpp -std=c++03 -o $1l -I. -Wall
if [  -e $1l ]; then
./$1l 
fi
rm $1l
echo "$ clang++ $1.cpp -std=2b -o $1l -I. -Wall"
clang++ $1.cpp -std=c++2b -o $1l -I. -Wall
if [  -e $1l ]; then
./$1l
fi
echo "\r"
echo "$ g++ $1.cpp -std=03 -o $1g -I. -Wall"
g++ $1.cpp -std=c++03 -o $1g -I. -Wall
if [ -e $1g ]; then
./$1g
fi
rm $1g
echo "\r"
echo "$ g++ $1.cpp -std=2b -o $1g -I. -Wall"
g++ $1.cpp -std=c++2b -o $1g -I. -Wall
if [ -e $1g ]; then
./$1g 
fi
```
## 編纂・実行結果(compile and go)

```ubuntu:bash
# ./clgc.sh  p256
rm: cannot remove 'p256l': No such file or directory
rm: cannot remove 'p256g': No such file or directory
$ clang++ p256.cpp -std=03 -o p256l -I. -Wall
In file included from p256.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 \
 ^
p256.cpp:26:15: error: expected template
       export module M:A;
              ^
p256.cpp:26:15: error: unknown type name 'module'
p256.cpp:26:23: error: expected ';' after top level declarator
       export module M:A;
                      ^
                      ;
p256.cpp:26:24: error: C++ requires a type specifier for all declarations
       export module M:A;
                       ^
p256.cpp:27:15: error: expected template
       export struct B;
              ^
p256.cpp:29:1: error: unknown type name 'module'
module M:B;
^
p256.cpp:29:9: error: expected ';' after top level declarator
module M:B;
        ^
        ;
p256.cpp:29:10: warning: declaration does not declare anything [-Wmissing-declarations]
module M:B;
         ^
p256.cpp:34:3: error: unknown type name 'module'
  module M:C;
  ^
p256.cpp:34:11: error: expected ';' after top level declarator
  module M:C;
          ^
          ;
p256.cpp:34:12: error: C++ requires a type specifier for all declarations
  module M:C;
           ^
p256.cpp:35:3: error: unknown type name 'import'
  import :A;
  ^
p256.cpp:35:10: error: expected unqualified-id
  import :A;
         ^
p256.cpp:38:10: error: expected template
  export module M;
         ^
p256.cpp:38:10: error: unknown type name 'module'
p256.cpp:39:10: error: expected template
  export import :A;
         ^
p256.cpp:39:10: error: unknown type name 'import'
p256.cpp:39:17: error: expected unqualified-id
  export import :A;
                ^
p256.cpp:40:3: error: unknown type name 'import'
  import :B;
  ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
1 warning and 20 errors generated.
rm: cannot remove 'p256l': No such file or directory
$ clang++ p256.cpp -std=2b -o p256l -I. -Wall
p256.cpp:26:23: error: sorry, module partitions are not yet supported
       export module M:A;
                      ^~
p256.cpp:26:15: error: module declaration must occur at the start of the translation unit
       export module M:A;
              ^
p256.cpp:1:1: note: add 'module;' to the start of the file to introduce a global module fragment
// C++N4910 Committee Draft, Standard for Programming Language C++
^
p256.cpp:29:9: error: sorry, module partitions are not yet supported
module M:B;
        ^~
p256.cpp:29:1: error: translation unit contains multiple module declarations
module M:B;
^
p256.cpp:26:15: note: previous module declaration is here
       export module M:A;
              ^
p256.cpp:34:11: error: sorry, module partitions are not yet supported
  module M:C;
          ^~
p256.cpp:34:3: error: translation unit contains multiple module declarations
  module M:C;
  ^
p256.cpp:26:15: note: previous module declaration is here
       export module M:A;
              ^
p256.cpp:35:10: error: sorry, module partitions are not yet supported
  import :A;
         ^~
p256.cpp:38:10: error: translation unit contains multiple module declarations
  export module M;
         ^
p256.cpp:26:15: note: previous module declaration is here
       export module M:A;
              ^
p256.cpp:39:17: error: sorry, module partitions are not yet supported
  export import :A;
                ^~
p256.cpp:40:10: error: sorry, module partitions are not yet supported
  import :B;
         ^~
p256.cpp:44:3: error: translation unit contains multiple module declarations
  module X;
  ^
p256.cpp:26:15: note: previous module declaration is here
       export module M:A;
              ^
p256.cpp:45:3: error: @import of module 'M' in implementation of 'M'; use #import
  import M;
  ^
p256.cpp:51:10: error: translation unit contains multiple module declarations
  export module A;
         ^
p256.cpp:26:15: note: previous module declaration is here
       export module M:A;
              ^
p256.cpp:55:3: error: translation unit contains multiple module declarations
  module B;
  ^
p256.cpp:26:15: note: previous module declaration is here
       export module M:A;
              ^
p256.cpp:56:10: fatal error: module 'A' not found
  import A;
  ~~~~~~~^
15 errors generated.

$ g++ p256.cpp -std=03 -o p256g -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from p256.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 \
      |  ^~~~~
p256.cpp:26:8: warning: keyword 'export' not implemented, and will be ignored
   26 |        export module M:A;
      |        ^~~~~~
p256.cpp:26:15: error: 'module' does not name a type
   26 |        export module M:A;
      |               ^~~~~~
p256.cpp:26:15: note: C++20 'module' only available with '-fmodules-ts'
p256.cpp:27:8: warning: keyword 'export' not implemented, and will be ignored
   27 |        export struct B;
      |        ^~~~~~
p256.cpp:29:1: error: 'module' does not name a type
   29 | module M:B;
      | ^~~~~~
p256.cpp:29:1: note: C++20 'module' only available with '-fmodules-ts'
p256.cpp:34:3: error: 'module' does not name a type
   34 |   module M:C;
      |   ^~~~~~
p256.cpp:34:3: note: C++20 'module' only available with '-fmodules-ts'
p256.cpp:35:10: error: found ':' in nested-name-specifier, expected '::'
   35 |   import :A;
      |          ^
      |          ::
p256.cpp:35:3: error: 'import' does not name a type
   35 |   import :A;
      |   ^~~~~~
p256.cpp:35:3: note: C++20 'import' only available with '-fmodules-ts'
p256.cpp:38:3: warning: keyword 'export' not implemented, and will be ignored
   38 |   export module M;
      |   ^~~~~~
p256.cpp:38:10: error: 'module' does not name a type
   38 |   export module M;
      |          ^~~~~~
p256.cpp:38:10: note: C++20 'module' only available with '-fmodules-ts'
p256.cpp:39:3: warning: keyword 'export' not implemented, and will be ignored
   39 |   export import :A;
      |   ^~~~~~
p256.cpp:39:17: error: found ':' in nested-name-specifier, expected '::'
   39 |   export import :A;
      |                 ^
      |                 ::
p256.cpp:39:10: error: 'import' does not name a type
   39 |   export import :A;
      |          ^~~~~~
p256.cpp:39:10: note: C++20 'import' only available with '-fmodules-ts'
p256.cpp:40:10: error: found ':' in nested-name-specifier, expected '::'
   40 |   import :B;
      |          ^
      |          ::
p256.cpp:40:3: error: 'import' does not name a type
   40 |   import :B;
      |   ^~~~~~
p256.cpp:40:3: note: C++20 'import' only available with '-fmodules-ts'
p256.cpp:42:3: warning: keyword 'export' not implemented, and will be ignored
   42 |   export void f(B b = B());
      |   ^~~~~~
p256.cpp:44:3: error: 'module' does not name a type
   44 |   module X;
      |   ^~~~~~
p256.cpp:44:3: note: C++20 'module' only available with '-fmodules-ts'
p256.cpp:45:3: error: 'import' does not name a type
   45 |   import M;
      |   ^~~~~~
p256.cpp:45:3: note: C++20 'import' only available with '-fmodules-ts'
p256.cpp:51:3: warning: keyword 'export' not implemented, and will be ignored
   51 |   export module A;
      |   ^~~~~~
p256.cpp:51:10: error: 'module' does not name a type
   51 |   export module A;
      |          ^~~~~~
p256.cpp:51:10: note: C++20 'module' only available with '-fmodules-ts'
p256.cpp:53:3: warning: keyword 'export' not implemented, and will be ignored
   53 |   export using Y = X;
      |   ^~~~~~
p256.cpp:53:16: error: expected nested-name-specifier before 'Y'
   53 |   export using Y = X;
      |                ^
p256.cpp:55:3: error: 'module' does not name a type
   55 |   module B;
      |   ^~~~~~
p256.cpp:55:3: note: C++20 'module' only available with '-fmodules-ts'
p256.cpp:56:3: error: 'import' does not name a type
   56 |   import A;
      |   ^~~~~~
p256.cpp:56:3: note: C++20 'import' only available with '-fmodules-ts'
p256.cpp:57:3: error: 'Y' does not name a type
   57 |   Y y;
      |   ^
rm: cannot remove 'p256g': No such file or directory

$ g++ p256.cpp -std=2b -o p256g -I. -Wall
p256.cpp:26:8: warning: keyword 'export' is enabled with '-fmodules-ts'
   26 |        export module M:A;
      |        ^~~~~~
p256.cpp:26:15: error: 'module' does not name a type
   26 |        export module M:A;
      |               ^~~~~~
p256.cpp:26:15: note: C++20 'module' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:27:8: warning: keyword 'export' is enabled with '-fmodules-ts'
   27 |        export struct B;
      |        ^~~~~~
p256.cpp:29:1: error: 'module' does not name a type
   29 | module M:B;
      | ^~~~~~
p256.cpp:29:1: note: C++20 'module' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:34:3: error: 'module' does not name a type
   34 |   module M:C;
      |   ^~~~~~
p256.cpp:34:3: note: C++20 'module' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:35:10: error: found ':' in nested-name-specifier, expected '::'
   35 |   import :A;
      |          ^
      |          ::
p256.cpp:35:3: error: 'import' does not name a type
   35 |   import :A;
      |   ^~~~~~
p256.cpp:35:3: note: C++20 'import' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:38:3: warning: keyword 'export' is enabled with '-fmodules-ts'
   38 |   export module M;
      |   ^~~~~~
p256.cpp:38:10: error: 'module' does not name a type
   38 |   export module M;
      |          ^~~~~~
p256.cpp:38:10: note: C++20 'module' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:39:3: warning: keyword 'export' is enabled with '-fmodules-ts'
   39 |   export import :A;
      |   ^~~~~~
p256.cpp:39:17: error: found ':' in nested-name-specifier, expected '::'
   39 |   export import :A;
      |                 ^
      |                 ::
p256.cpp:39:10: error: 'import' does not name a type
   39 |   export import :A;
      |          ^~~~~~
p256.cpp:39:10: note: C++20 'import' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:40:10: error: found ':' in nested-name-specifier, expected '::'
   40 |   import :B;
      |          ^
      |          ::
p256.cpp:40:3: error: 'import' does not name a type
   40 |   import :B;
      |   ^~~~~~
p256.cpp:40:3: note: C++20 'import' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:42:3: warning: keyword 'export' is enabled with '-fmodules-ts'
   42 |   export void f(B b = B());
      |   ^~~~~~
p256.cpp:44:3: error: 'module' does not name a type
   44 |   module X;
      |   ^~~~~~
p256.cpp:44:3: note: C++20 'module' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:45:3: error: 'import' does not name a type
   45 |   import M;
      |   ^~~~~~
p256.cpp:45:3: note: C++20 'import' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:51:3: warning: keyword 'export' is enabled with '-fmodules-ts'
   51 |   export module A;
      |   ^~~~~~
p256.cpp:51:10: error: 'module' does not name a type
   51 |   export module A;
      |          ^~~~~~
p256.cpp:51:10: note: C++20 'module' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:53:3: warning: keyword 'export' is enabled with '-fmodules-ts'
   53 |   export using Y = X;
      |   ^~~~~~
p256.cpp:55:3: error: 'module' does not name a type
   55 |   module B;
      |   ^~~~~~
p256.cpp:55:3: note: C++20 'module' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
p256.cpp:56:3: error: 'import' does not name a type
   56 |   import A;
      |   ^~~~~~
p256.cpp:56:3: note: C++20 'import' only available with '-fmodules-ts', which is not yet enabled with '-std=c++20'
```

## 検討事項(agenda)
コンパイルエラーの理由を解説する。

<|--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

## 自己参照(self reference)

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


 ＜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。＞

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