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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3 章 現代の C++ への移行
項目 15：可能な場面では常に constexpr を用いる
C++11 で最も混乱する新用語を表彰すれば、恐らく constexpr が受賞するでしょう。オブジェク
トに使用すれば本質的な意味は強化された const ですが、関数に使用した場合の意味は大きく異な
ります。この混乱はくぐり抜ける価値があります。表現したい内容が constexpr にふさわしい場面
では、間違いなく使用したくなるでしょう。
constexpr は、その値が単なる定数というよりも、コンパイル時に既知の定数であることを概念
的に表現します。この基礎概念から出発し、関数に対し constexpr を用いた場合は他にも多くの
ニュアンスを含みます。お楽しみの結末をばらさないように、ここでは constexpr 関数の実行結果
は const である、またはその値がコンパイル時に既知である、などとは想定できないとだけ述べて
おきます。恐らく最も興味を引かれる点は、これらの動作が仕様（feature）であるとされている点
でしょう。constexpr 関数は、const な結果を返さなくとも、またコンパイル時に既知でなくとも
良いのです！
まずは constexpr オブジェクトから始めましょう。constexpr オブジェクトは事実上 const
ですし、またコンパイル時に既知の値を保持します（厳密に言えば、値が決定されるのは翻訳
（translation）時です。また翻訳処理はコンパイル時
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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.