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+ < span itemprop ="name "> 関数宣言を削除する理由を指定できるようにする [P2573R2]</ span >
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+ 最終更新日時(UTC):
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+ < span itemprop ="datePublished " content ="2024-09-13T03:00:43 ">
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+ 2024年09月13日 03時00分43秒
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+ </ span >
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+ < br />
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+ < span itemprop ="author " itemscope itemtype ="http://schema.org/Person ">
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+ < span itemprop ="name "> Akira Takahashi</ span >
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+ が更新
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+ < p class ="text-right ">
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+ < a class ="history " target ="_blank " href ="https://github.com/cpprefjp/site/commits/master/lang/cpp26/delete_reason.md ">
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+ < span class ="fa fa-fw fa-clock-o fa-flip-horizontal "> </ span > 履歴
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+ </ a >
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+ < a class ="edit " target ="_blank " href ="https://github.com/cpprefjp/site/edit/master/lang/cpp26/delete_reason.md ">
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+ < span class ="fa fa-fw fa-pencil "> </ span > 編集
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+ </ p >
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+ < div class ="row ">
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+ < div class ="col-sm-12 content-body ">
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+ < h1 itemprop ="name "> < span class ="token "> 関数宣言を削除する理由を指定できるようにする [P2573R2]</ span > < span class ="cpp cpp26 " title ="C++26で追加 "> (C++26)</ span > </ h1 >
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+ < div itemprop ="articleBody "> < p > </ p >
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+ < p > このページはC++26に採用される見込みの言語機能の変更を解説しています。</ p >
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+ < p > のちのC++規格でさらに変更される場合があるため< a href ="#relative-page "> 関連項目</ a > を参照してください。</ p >
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+ < p > </ p >
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+ < h2 > 概要</ h2 >
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+ < p > C++26では、関数をdelte宣言する際に、その理由をコンパイル時文字列で指定できるようになる。</ p >
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+ < p > < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="c1 "> // 別名の新たなAPIを用意する場合に、そちらに誘導する</ span >
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+ < span class ="kt "> void</ span > < span class ="nf "> newapi</ span > < span class ="p "> ();</ span >
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+ < span class ="kt "> void</ span > < span class ="nf "> oldapi</ span > < span class ="p "> ()</ span > < span class ="o "> =</ span > < span class ="k "> delete</ span > < span class ="p "> (</ span > < span class ="s "> "This old API is outdated and already been removed. Please use newapi() instead."</ span > < span class ="p "> );</ span >
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+
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+ < span class ="k "> template</ span > < span class ="o "> <</ span > < span class ="k "> typename</ span > < span class ="n "> T</ span > < span class ="o "> ></ span >
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+ < span class ="k "> struct</ span > < span class ="n "> A</ span > < span class ="p "> {</ span > < span class ="cm "> /* … */</ span > < span class ="p "> };</ span >
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+
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+ < span class ="c1 "> // 一部のオーバーロードが危険であるために禁止する場合</ span >
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+ < span class ="k "> template</ span > < span class ="o "> <</ span > < span class ="k "> typename</ span > < span class ="n "> T</ span > < span class ="o "> ></ span >
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+ < span class ="n "> A</ span > < span class ="o "> <</ span > < span class ="n "> T</ span > < span class ="o "> ></ span > < span class ="n "> factory</ span > < span class ="p "> (</ span > < span class ="k "> const</ span > < span class ="n "> T</ span > < span class ="o "> &</ span > < span class ="p "> )</ span > < span class ="p "> {</ span > < span class ="cm "> /* process lvalue */</ span > < span class ="p "> }</ span >
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+ < span class ="k "> template</ span > < span class ="o "> <</ span > < span class ="k "> typename</ span > < span class ="n "> T</ span > < span class ="o "> ></ span >
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+ < span class ="n "> A</ span > < span class ="o "> <</ span > < span class ="n "> T</ span > < span class ="o "> ></ span > < span class ="n "> factory</ span > < span class ="p "> (</ span > < span class ="k "> const</ span > < span class ="n "> T</ span > < span class ="o "> &&</ span > < span class ="p "> )</ span > < span class ="o "> =</ span > < span class ="k "> delete</ span > < span class ="p "> (</ span > < span class ="s "> "Using rvalue to construct A may result in dangling reference"</ span > < span class ="p "> );</ span >
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+
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+ < span class ="c1 "> // 一部の自動定義される特殊メンバ関数が</ span >
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+ < span class ="c1 "> // 低パフォーマンスを引き起こすために禁止する場合</ span >
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+ < span class ="k "> struct</ span > < span class ="n "> MoveOnly</ span > < span class ="p "> {</ span >
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+ < span class ="c1 "> // … (with move members defaulted or defined)</ span >
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+ < span class ="n "> MoveOnly</ span > < span class ="p "> (</ span > < span class ="k "> const</ span > < span class ="n "> MoveOnly</ span > < span class ="o "> &</ span > < span class ="p "> )</ span > < span class ="o "> =</ span > < span class ="k "> delete</ span > < span class ="p "> (</ span > < span class ="s "> "Copy-construction is expensive; please use move construction instead."</ span > < span class ="p "> );</ span >
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+ < span class ="n "> MoveOnly</ span > < span class ="o "> &</ span > < span class ="k "> operator</ span > < span class ="o "> =</ span > < span class ="p "> (</ span > < span class ="k "> const</ span > < span class ="n "> MoveOnly</ span > < span class ="o "> &</ span > < span class ="p "> )</ span > < span class ="o "> =</ span > < span class ="k "> delete</ span > < span class ="p "> (</ span > < span class ="s "> "Copy-assignment is expensive; please use move assignment instead."</ span > < span class ="p "> );</ span >
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+ < span class ="p "> };</ span >
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+ </ code > </ pre > </ div >
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+ </ p >
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+ < p > これまでは削除理由を指定できなかったために、ユーザーが誤って削除済み関数にアクセスした際に「エラー!:削除された関数を呼び出そうとした」という情報しか得られなかった。削除理由が指定できるようになることで、その設計意図をユーザーに伝えられるようになる。</ p >
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+ < h2 > < a href ="#relative-page " id ="relative-page "> 関連項目</ a > </ h2 >
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+ < ul >
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+ < li > < a href ="../cpp11/defaulted_and_deleted_functions.html "> C++11 関数のdefault/delete宣言</ a > </ li >
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+ </ ul >
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+ < h2 > 参照</ h2 >
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+ < ul >
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+ < li > < a href ="https://open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2573r2.html " target ="_blank "> P2573R2 < code > = delete("should have a reason");</ code > </ a > </ li >
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