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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24
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1 章 型推論
•
名前ではなく、型を T とする左辺値式については、常に T& という型を返す。
•
C++14 では decltype(auto) が追加された。auto のように初期化子から型を推論するが、適
用される推論規則は decltype のものである。
項目 4：推論された型を確認する
推論した型を表示、確認する方法は複数あり、開発プロセスの段階に応じ変化します。ここでは
3 種類の方法を取り上げます。コーディング時に型推論情報を得る、コンパイル時に得る、実行時
に得る、の 3 つです。
IDE のエディタ
IDE のエディタは、マウスカーソルを乗せるだけでプログラムエンティティ（変数、仮引数、関数
など）の型を表示する機能を備えているのが一般的です。例えば、次のようなコードがあるとしま
しょう8。
const int theAnswer = 42;
auto x = theAnswer;
auto y = &theAnswer;
IDE のエディタは恐らく、x に推論した型を int、y については const int* と表示するでしょう。
この動作を実現するには開発中のコードが多かれ少なかれコンパイル可能な状態でなければなり
ません。IDE が型推論情報を表示できるのは、内部で C++ コンパイラを実行しているためです（も
しくは、少なくともコンパイラのフロントエンド）。コンパイラがコードを構文解析、型推論できな
ければ型を表示できません。
int のような単純（組み込み）型では、IDE
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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.