April 2022
Beginner to intermediate
464 pages
6h 44m
Japanese
Content preview from 実用 Go言語 ―システム開発の現場で知っておきたいアドバイス
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4.4 インタフェースの合成
Goの標準ライブラリに含まれるio.ReadWriterは次のように宣言されています。これは構造体の埋め込みと似たような記法です。この場合はio.Readerが満たすべきインタフェース（Read()メソッド）と、io.Writerが満たすべきインタフェース（Write()メソッド）の両方を満たさなければならないインタフェースになります。
type ReadWriter interface {
Reader
Writer
}
Javaを知っている読者には「Javaのインタフェースの多重継承と同じ」と言えばわかりやすいでしょう。
Goのエコシステムでは、なるべく最小のインタフェースを定義し、それを組み合わせたインタフェースを合成して利用します。ただし、それは言語的な制約のせいでもありました。バージョン1.13までのGoでは、合成するインタフェースに重複するメソッドがあるとエラーになっていました。Go 1.14以降はエラーではなくなったので、エラー回避のために細かくインタフェースを区切る必要はなくなりました。
それでも、必要最小限のメソッドを持ったインタフェースを使う方が、依存関係がクリアになり、また少ないメソッド定義だけで利用できるので便利です。必要以上にメソッドが多いインタフェース（制約の厳しいインタフェース）は使わない方が良いでしょう。
たとえば、外部からの読み込みにio.ReadSeeker1を指定したとします。ここに、HTTPリクエストのボディを渡した場合にはエラーとなって利用できません。一度コンテンツをメモリに展開し、すべてのインタフェースを満たした ...
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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.