September 2015
Intermediate to advanced
364 pages
10h 33m
Japanese
Content preview from Effective Modern C++ ―C++11/14プログラムを進化させる42項目
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180
｜
5 章 右辺値参照、ムーブセマンティクス、完全転送
このことは、値戻しをする関数内で戻り値となるローカルオブジェクトを std::move すると、コ
ンパイラを手助けすることにはならず（コンパイラは、コピーを省略しない場合、このローカルオ
ブジェクトを右辺値として扱わなければならない）、逆に間違いなく妨げになることを意味します
（RVO を妨げる）。ローカルオブジェクトを std::move するのが適切な場面もありますが（今後使
わないことが確実なローカルオブジェクトを関数に渡す場合）、return 文の一部として RVO 不可能
な場面や、値を渡した仮引数を返す場合は、適切ではありません。
重要ポイント
•
std::move は右辺値参照に対し、また std::forward は最後に使用するユニヴァーサル参照
に対し、それぞれ実行する。
•
値戻しする関数から返す右辺値参照、ユニヴァーサル参照についても同様のことが言える。
•
戻り値の最適化にそぐわないローカルオブジェクトに対し、std::move や std::forward を
実行してはいけない。
項目 26：ユニヴァーサル参照をとるオーバロードは避ける
仮引数に名前をとり、日付と時刻をログ出力し、名前をグローバルデータに追加する関数を開発
するとしましょう。まず浮かぶのは次のような関数でしょう。
std::multiset<std::string> names; // global data structure
グローバルデータ
void
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.