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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

C++N4606(198)14.7.2 Explicit instantiation [temp.explicit]p397

Posted at

#はじめに
N4606 Working Draft, Standard for Programming Language C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/#mailing2016-11
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf

n4606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。

##作業方針
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。

list

N4606 Working Draft 2016, ISO/IEC 14882, C++ standard(1) coding list
https://qiita.com/kaizen_nagoya/items/df5d62c35bd6ed1c3d43/

Compiler

###clang++ --version
clang version 6.0.0 (tags/RELEASE_600/final)
Target: x86_64-apple-darwin17.4.0

###g++-7 --version
g++-7 (Homebrew GCC 7.3.0_1) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.

#(198)14.7.2 Explicit instantiation [temp.explicit]p397

p398.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf
#define msg "(198)14.7.2 Explicit instantiation [temp.explicit]p397.cpp"
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>

Example:
template<class T> class Array { void mf(); };
template class Array<char>;
template void Array<int>::mf();
template<class T> void sort(Array<T>& v) { /* ... */ }
template void sort(Array<char>&); // argument is deduced here
namespace N {
template<class T> void f(T&) { }
}
template void N::f<int>(int&);
—end example ]
4 A declaration of a function template, a variable template, a member function or static data member of a class
template, or a member function template of a class or class template shall precede an explicit instantiation of
that entity. A definition of a class template, a member class of a class template, or a member class template of
a class or class template shall precede an explicit instantiation of that entity unless the explicit instantiation
is preceded by an explicit specialization of the entity with the same template arguments. If the declaration of
the explicit instantiation names an implicitly-declared special member function (Clause 12), the program is
ill-formed.
5 For a given set of template arguments, if an explicit instantiation of a template appears after a declaration of
an explicit specialization for that template, the explicit instantiation has no effect. Otherwise, for an explicit
instantiation definition the definition of a function template, a variable template, a member function template,
or a member function or static data member of a class template shall be present in every translation unit in
which it is explicitly instantiated.
§ 14.7.2 397
©ISO/IEC N4606
6 An explicit instantiation of a class, function template, or variable template specialization is placed in the
namespace in which the template is defined. An explicit instantiation for a member of a class template is
placed in the namespace where the enclosing class template is defined. An explicit instantiation for a member
template is placed in the namespace where the enclosing class or class template is defined. [ Example:
namespace N {
template<class T> class Y { void mf() { } };
}
template class Y<int>; // error: class template Y not visible
// in the global namespace
using N::Y;
template class Y<int>; // error: explicit instantiation outside of the
// namespace of the template
template class N::Y<char*>; // OK: explicit instantiation in namespace N
template void N::Y<double>::mf(); // OK: explicit instantiation
// in namespace N
—end example ]
7 A trailing template-argument can be left unspecified in an explicit instantiation of a function template
specialization or of a member function template specialization provided it can be deduced from the type of a
function parameter (14.8.2). [ Example:
template<class T> class Array { /* ... */ };
template<class T> void sort(Array<T>& v) { /* ... */ }
// instantiate sort(Array<int>&) - template-argument deduced
template void sort<>(Array<int>&);
—end example ]
8 An explicit instantiation that names a class template specialization is also an explicit instantiation of the
same kind (declaration or definition) of each of its members (not including members inherited from base
classes and members that are templates) that has not been previously explicitly specialized in the translation
unit containing the explicit instantiation, except as described below. [ Note: In addition, it will typically be
an explicit instantiation of certain implementation-dependent data about the class. —end note ]
9 An explicit instantiation definition that names a class template specialization explicitly instantiates the class
template specialization and is an explicit instantiation definition of only those members that have been
defined at the point of instantiation.
10 Except for inline functions and variables, declarations with types deduced from their initializer or return
value (7.1.7.4), const variables of literal types, variables of reference types, and class template specializations,
explicit instantiation declarations have the effect of suppressing the implicit instantiation of the entity to
which they refer. [ Note: The intent is that an inline function that is the subject of an explicit instantiation
declaration will still be implicitly instantiated when odr-used (3.2) so that the body can be considered for
inlining, but that no out-of-line copy of the inline function would be generated in the translation unit.—end
note ]
11 If an entity is the subject of both an explicit instantiation declaration and an explicit instantiation definition
in the same translation unit, the definition shall follow the declaration. An entity that is the subject of
an explicit instantiation declaration and that is also used in a way that would otherwise cause an implicit
instantiation (14.7.1) in the translation unit shall be the subject of an explicit instantiation definition
somewhere in the program; otherwise the program is ill-formed, no diagnostic required. [ Note: This rule
§ 14.7.2 398
©ISO/IEC N4606
does apply to inline functions even though an explicit instantiation declaration of such an entity has no other
normative effect. This is needed to ensure that if the address of an inline function is taken in a translation
unit in which the implementation chose to suppress the out-of-line body, another translation unit will supply
the body.—end note ] An explicit instantiation declaration shall not name a specialization of a template
with internal linkage.
12 The usual access checking rules do not apply to names used to specify explicit instantiations. [ Note: In
particular, the template arguments and names used in the function declarator (including parameter types,
return types and exception specifications) may be private types or objects which would normally not be
accessible and the template may be a member template or member function which would not normally be
accessible. —end note ]
13 An explicit instantiation does not constitute a use of a default argument, so default argument instantiation is
not done. [ Example:
char* p = 0;
template<class T> T g(T x = &p) { return x; }
template int g<int>(int); // OK even though &p isn’t an int.
—end examp
int main() {
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p360
$ clang++ p360.cpp
(176)14.5.1.2 Member classes of class templates [temp.mem.class]p360.cpp

$ g++-7 p360.cpp
(176)14.5.1.2 Member classes of class templates [temp.mem.class]p360.cpp

タブを２つの空白に変換しているスクリプトは下記。

a.sh
#!/bin/bash
astyle -s2 -c < $1.cpp > $1s2.cpp
cat $1s2.cpp

#検討事項
役に立つまたは意味のある出力

#参考資料

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

Qiitaに投稿するCのStyle例(暫定)
https://qiita.com/kaizen_nagoya/items/946df1528a6a1ef2bc0d

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
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

#文書履歴
0.10 初稿 2080420

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