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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293
8 章
もう一ひねり
C++ の汎用的な技法や機能に共通して言えることですが、使用するにふさわしい場面もあれば、ふ
さわしくない場面もあります。汎用的な技法や機能が有用である場面の解説は通常きわめて直観的
で分かりやすいものですが、本章では分かりにくいものを 2 つとりあげます。汎用技法としての値
渡しと、汎用機能としての直接配置（emplacement）です。これらを使用するにふさわしいか否か
を判断するには、多くの要因が関係します。著者から言える最も良い助言はその使用を熟慮せよ、
です。そうは言っても、この 2 つは効率的かつ現代の C++ プログラミング（effective modern C++
programming）で重要な役割を担いますから、読者のソフトウェア開発現場でのこの 2 つの使用が
適切か否かを判断する目安をここで述べます。
項目 41：コピー可能仮引数のムーブコストが安く、かつ常にコピー
する場面では値渡しを検討する
関数仮引数にはコピーを想定したものもあります1。例えば、addName というメンバ関数が、その
仮引数をローカルなコンテナにコピーするとします。効率を考えれば、このような関数では実引数
が左辺値ならばコピー、右辺値ならばムーブするべきです。
class Widget {
public: 左辺値を受け取る
void addName(const std::string& newName) // take lvalue;
{ names.push_back(newName); ...
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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.