13.7.4 Variadic templates [temp.variadic] C++N4910:2022 (217) p378.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.

# 13.7.4 Variadic templates [temp.variadic] C++N4910:2022 (217) p378.cpp

## 算譜(source code)

```c++:p378.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 = "13.7.4 Variadic templates [temp.variadic] C++N4910:2022 (217) p378.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 <typeinfo>

using namespace std;

// Example 1
template<class ... Types> struct Tuple { };
Tuple<> t0;
Tuple<int> t1;
Tuple<int, float> t2;
Tuple<0> error;
// Types contains no arguments
// Types contains one argument: int
// Types contains two arguments: int and float // error: 0 is not a type
// [Example 2:
template<class ... Types> void f(Types ... args);
f();
f(1);
f(2, 1.0);
// args contains no arguments
// args contains one argument: int
// args contains two arguments: int and double
// [Example 3:
template <typename... Args>
void foo(Args... args) {
    [...xs=args] {
        bar(xs...);
    };
}
foo();
foo(1);
// xs is an init-capture pack
// xs contains zero init-captures // xs contains one init-capture
// [Example 4:
template<class ... Types> void f4(Types ... rest);
template<class ... Types> void g(Types ... rest) {
    f4(&rest ...); // &rest ...is a pack expansion; &rest is its pattern
}
// [Example 5:
template<typename...> struct Tuple {};
template<typename T1, typename T2> struct Pair {};
template<class ... Args1> struct zip {
    template<class ... Args2> struct with {
        typedef Tuple<Pair<Args1, Args2> ... > type;
    };
};
typedef zip<short, int>::with<unsigned short, unsigned>::type T1; // T1 is Tuple<Pair<short, unsigned short>, Pair<int, unsigned>>
typedef zip<short>::with<unsigned short, unsigned>::type T2;
// error: different number of arguments specified for Args1 and Args2
template<class ... Args>
void g5(Args ... args) {
    f5(const_cast<const Args*>(&args)...);
    f5(5 ...);
    f5(args);
    f5(h(args ...) + args ...);
}
// OK, Args is expanded by the function parameter pack args // OK, “Args” and “args” are expanded
// error: pattern does not contain any packs
// error: pack “args” is not expanded
// OK, first “args” expanded within h, // second “args” expanded within f
// [Example 6:
template<typename ...Args>
bool all(Args ...args) {
    return (... && args);
}
bool b = all(true, true, true, false);
// Within the instantiation of all, the returned expression expands to ((true && true) && true) && false, which evaluates to false.
// [Example 7:
template<class... T> struct X : T... { };
template<class... T> void f(T... values) {
    X<T...> x(values...);
}
template void f7<>();
// OK, X<> has no base classes
// x is a variable of type X<> that is value-initialized
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 p378
$ clang++ p378.cpp -std=c++03 -o p378l -I. -Wall
In file included from p378.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 \
 ^
p378.cpp:26:17: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
 template<class ... Types> struct Tuple { };
                ^
p378.cpp:30:7: error: template argument for template type parameter must be a type
Tuple<0> error;
      ^
p378.cpp:26:21: note: template parameter is declared here
 template<class ... Types> struct Tuple { };
                    ^
p378.cpp:35:16: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class ... Types> void f(Types ... args);
               ^
p378.cpp:36:1: error: C++ requires a type specifier for all declarations
f();
^
p378.cpp:37:1: error: C++ requires a type specifier for all declarations
f(1);
^
p378.cpp:38:1: error: C++ requires a type specifier for all declarations
f(2, 1.0);
^
p378.cpp:43:21: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template <typename... Args>
                    ^
p378.cpp:45:7: error: expected expression
      [...xs=args]{
      ^
p378.cpp:48:3: error: C++ requires a type specifier for all declarations
  foo();
  ^
p378.cpp:49:3: error: C++ requires a type specifier for all declarations
  foo(1);
  ^
p378.cpp:53:18: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template<class ... Types> void f4(Types ... rest);
                 ^
p378.cpp:54:18: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template<class ... Types> void g(Types ... rest) {
                 ^
p378.cpp:58:18: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<typename...> struct Tuple {};
                 ^
p378.cpp:58:30: error: redefinition of 'Tuple'
template<typename...> struct Tuple {};
                             ^
p378.cpp:26:35: note: previous definition is here
 template<class ... Types> struct Tuple { };
                                  ^
p378.cpp:60:16: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<class ... Args1> struct zip {
               ^
p378.cpp:61:18: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template<class ... Args2> struct with {
                 ^
p378.cpp:62:38: error: pack expansion contains parameter packs 'Args1' and 'Args2' that have different lengths (1 vs. 2)
    typedef Tuple<Pair<Args1, Args2> ... > type;
                       ~~~~~  ~~~~~  ^
p378.cpp:66:21: note: in instantiation of template class 'zip<short>::with<unsigned short, unsigned int>' requested here
typedef zip<short>::with<unsigned short, unsigned>::type T2;
                    ^
p378.cpp:68:18: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template<class ... Args>
                 ^
p378.cpp:71:12: error: pack expansion does not contain any unexpanded parameter packs
      f5(5 ...);
         ~ ^
p378.cpp:72:7: error: expression contains unexpanded parameter pack 'args'
      f5(args);
      ^  ~~~~
p378.cpp:80:19: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
template<typename ...Args>
                  ^
p378.cpp:81:38: warning: pack fold expression is a C++17 extension [-Wc++17-extensions]
    bool all(Args ...args) { return (... && args); }
                                     ^
p378.cpp:85:17: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template<class... T> struct X : T... { };
                ^
p378.cpp:86:17: warning: variadic templates are a C++11 extension [-Wc++11-extensions]
  template<class... T> void f(T... values) {
                ^
p378.cpp:89:17: error: explicit instantiation of 'f7' does not refer to a function template, variable template, member function, member class, or static data member
  template void f7<>();
                ^
13 warnings and 13 errors generated.
rm: cannot remove 'p378l': No such file or directory
$ clang++ p378.cpp -std=c++2b -o p378l -I. -Wall
p378.cpp:30:7: error: template argument for template type parameter must be a type
Tuple<0> error;
      ^
p378.cpp:26:21: note: template parameter is declared here
 template<class ... Types> struct Tuple { };
                    ^
p378.cpp:36:1: error: C++ requires a type specifier for all declarations
f();
^
p378.cpp:37:1: error: C++ requires a type specifier for all declarations
f(1);
^
p378.cpp:38:1: error: C++ requires a type specifier for all declarations
f(2, 1.0);
^
p378.cpp:48:3: error: C++ requires a type specifier for all declarations
  foo();
  ^
p378.cpp:49:3: error: C++ requires a type specifier for all declarations
  foo(1);
  ^
p378.cpp:58:30: error: redefinition of 'Tuple'
template<typename...> struct Tuple {};
                             ^
p378.cpp:26:35: note: previous definition is here
 template<class ... Types> struct Tuple { };
                                  ^
p378.cpp:62:38: error: pack expansion contains parameter packs 'Args1' and 'Args2' that have different lengths (1 vs. 2)
    typedef Tuple<Pair<Args1, Args2> ... > type;
                       ~~~~~  ~~~~~  ^
p378.cpp:66:21: note: in instantiation of template class 'zip<short>::with<unsigned short, unsigned int>' requested here
typedef zip<short>::with<unsigned short, unsigned>::type T2;
                    ^
p378.cpp:71:12: error: pack expansion does not contain any unexpanded parameter packs
      f5(5 ...);
         ~ ^
p378.cpp:72:7: error: expression contains unexpanded parameter pack 'args'
      f5(args);
      ^  ~~~~
p378.cpp:89:17: error: explicit instantiation of 'f7' does not refer to a function template, variable template, member function, member class, or static data member
  template void f7<>();
                ^
11 errors generated.

$ g++ p378.cpp -std=c++03 -o p378g -I. -Wall
In file included from /usr/local/include/c++/12.1.0/atomic:38,
                 from p378.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 \
      |  ^~~~~
p378.cpp:26:17: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   26 |  template<class ... Types> struct Tuple { };
      |                 ^~~
p378.cpp:30:8: error: type/value mismatch at argument 1 in template parameter list for 'template<class ... Types> struct Tuple'
   30 | Tuple<0> error;
      |        ^
p378.cpp:30:8: note:   expected a type, got '0'
p378.cpp:35:16: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   35 | template<class ... Types> void f(Types ... args);
      |                ^~~
p378.cpp:35:44: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   35 | template<class ... Types> void f(Types ... args);
      |                                            ^~~~
p378.cpp:36:4: error: expected constructor, destructor, or type conversion before ';' token
   36 | f();
      |    ^
p378.cpp:37:2: error: expected constructor, destructor, or type conversion before '(' token
   37 | f(1);
      |  ^
p378.cpp:38:2: error: expected constructor, destructor, or type conversion before '(' token
   38 | f(2, 1.0);
      |  ^
p378.cpp:43:21: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   43 |   template <typename... Args>
      |                     ^~~
p378.cpp:44:20: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   44 |   void foo(Args... args) {
      |                    ^~~~
p378.cpp: In function 'void foo(Args ...)':
p378.cpp:45:8: warning: pack init-capture only available with '-std=c++20' or '-std=gnu++20' [-Wc++20-extensions]
   45 |       [...xs=args]{
      |        ^~~
p378.cpp:45:11: warning: lambda capture initializers only available with '-std=c++14' or '-std=gnu++14' [-Wc++14-extensions]
   45 |       [...xs=args]{
      |           ^~
p378.cpp:47:1: warning: lambda expressions only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   47 | }; }
      | ^
p378.cpp: At global scope:
p378.cpp:48:8: error: expected constructor, destructor, or type conversion before ';' token
   48 |   foo();
      |        ^
p378.cpp:49:6: error: expected constructor, destructor, or type conversion before '(' token
   49 |   foo(1);
      |      ^
p378.cpp:53:18: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   53 |   template<class ... Types> void f4(Types ... rest);
      |                  ^~~
p378.cpp:53:47: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   53 |   template<class ... Types> void f4(Types ... rest);
      |                                               ^~~~
p378.cpp:54:18: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   54 |   template<class ... Types> void g(Types ... rest) {
      |                  ^~~
p378.cpp:54:46: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   54 |   template<class ... Types> void g(Types ... rest) {
      |                                              ^~~~
p378.cpp:58:18: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   58 | template<typename...> struct Tuple {};
      |                  ^~~
p378.cpp:58:30: error: redefinition of 'struct Tuple<Types>'
   58 | template<typename...> struct Tuple {};
      |                              ^~~~~
p378.cpp:26:35: note: previous definition of 'struct Tuple<Types>'
   26 |  template<class ... Types> struct Tuple { };
      |                                   ^~~~~
p378.cpp:60:16: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   60 | template<class ... Args1> struct zip {
      |                ^~~
p378.cpp:61:18: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   61 |   template<class ... Args2> struct with {
      |                  ^~~
p378.cpp: In instantiation of 'struct zip<short int>::with<short unsigned int, unsigned int>':
p378.cpp:66:51:   required from here
p378.cpp:62:44: error: mismatched argument pack lengths while expanding 'Pair<Args1, Args2>'
   62 |     typedef Tuple<Pair<Args1, Args2> ... > type;
      |                                            ^~~~
p378.cpp:68:18: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   68 |   template<class ... Args>
      |                  ^~~
p378.cpp:69:22: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   69 |     void g5(Args ... args) {
      |                      ^~~~
p378.cpp: In function 'void g5(Args ...)':
p378.cpp:71:12: error: expansion pattern '5' contains no parameter packs
   71 |       f5(5 ...);
      |            ^~~
p378.cpp:71:7: error: there are no arguments to 'f5' that depend on a template parameter, so a declaration of 'f5' must be available [-fpermissive]
   71 |       f5(5 ...);
      |       ^~
p378.cpp:71:7: note: (if you use '-fpermissive', G++ will accept your code, but allowing the use of an undeclared name is deprecated)
p378.cpp:72:9: error: parameter packs not expanded with '...':
   72 |       f5(args);
      |       ~~^~~~~~
p378.cpp:72:9: note:         'args'
p378.cpp: At global scope:
p378.cpp:80:19: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   80 | template<typename ...Args>
      |                   ^~~
p378.cpp:81:22: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   81 |     bool all(Args ...args) { return (... && args); }
      |                      ^~~~
p378.cpp: In function 'bool all(Args ...)':
p378.cpp:81:45: warning: fold-expressions only available with '-std=c++17' or '-std=gnu++17' [-Wc++17-extensions]
   81 |     bool all(Args ...args) { return (... && args); }
      |                                             ^~~~
p378.cpp: At global scope:
p378.cpp:85:17: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   85 |   template<class... T> struct X : T... { };
      |                 ^~~
p378.cpp:86:17: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   86 |   template<class... T> void f(T... values) {
      |                 ^~~
p378.cpp:86:36: warning: variadic templates only available with '-std=c++11' or '-std=gnu++11' [-Wc++11-extensions]
   86 |   template<class... T> void f(T... values) {
      |                                    ^~~~~~
p378.cpp:89:17: error: variable or field 'f7' declared void
   89 |   template void f7<>();
      |                 ^~
p378.cpp:89:19: error: expected ';' before '<' token
   89 |   template void f7<>();
      |                   ^
      |                   ;
rm: cannot remove 'p378g': No such file or directory

$ g++ p378.cpp -std=c++2b -o p378g -I. -Wall
p378.cpp:30:8: error: type/value mismatch at argument 1 in template parameter list for 'template<class ... Types> struct Tuple'
   30 | Tuple<0> error;
      |        ^
p378.cpp:30:8: note:   expected a type, got '0'
p378.cpp:36:4: error: expected constructor, destructor, or type conversion before ';' token
   36 | f();
      |    ^
p378.cpp:37:2: error: expected constructor, destructor, or type conversion before '(' token
   37 | f(1);
      |  ^
p378.cpp:38:2: error: expected constructor, destructor, or type conversion before '(' token
   38 | f(2, 1.0);
      |  ^
p378.cpp:48:8: error: expected constructor, destructor, or type conversion before ';' token
   48 |   foo();
      |        ^
p378.cpp:49:6: error: expected constructor, destructor, or type conversion before '(' token
   49 |   foo(1);
      |      ^
p378.cpp:58:30: error: redefinition of 'struct Tuple<Types>'
   58 | template<typename...> struct Tuple {};
      |                              ^~~~~
p378.cpp:26:35: note: previous definition of 'struct Tuple<Types>'
   26 |  template<class ... Types> struct Tuple { };
      |                                   ^~~~~
p378.cpp: In instantiation of 'struct zip<short int>::with<short unsigned int, unsigned int>':
p378.cpp:66:51:   required from here
p378.cpp:62:44: error: mismatched argument pack lengths while expanding 'Pair<Args1, Args2>'
   62 |     typedef Tuple<Pair<Args1, Args2> ... > type;
      |                                            ^~~~
p378.cpp: In function 'void g5(Args ...)':
p378.cpp:71:12: error: expansion pattern '5' contains no parameter packs
   71 |       f5(5 ...);
      |            ^~~
p378.cpp:71:7: error: there are no arguments to 'f5' that depend on a template parameter, so a declaration of 'f5' must be available [-fpermissive]
   71 |       f5(5 ...);
      |       ^~
p378.cpp:71:7: note: (if you use '-fpermissive', G++ will accept your code, but allowing the use of an undeclared name is deprecated)
p378.cpp:72:9: error: parameter packs not expanded with '...':
   72 |       f5(args);
      |       ~~^~~~~~
p378.cpp:72:9: note:         'args'
p378.cpp: At global scope:
p378.cpp:89:17: error: 'f7' is not a function template
   89 |   template void f7<>();
      |                 ^~~~
```

## 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

## 自己参照(self reference)

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


 ＜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 　20220705