January 2014
Intermediate to advanced
352 pages
6h 34m
Japanese
Content preview from JavaScriptで学ぶ関数型プログラミング
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238
8 章 フローベースプログラミング
8.2
パイプライン
チェーンはオブジェクトやメソッド呼び出し周りの「流暢な」
API
を構築するため
に有用なパターンですが、関数型
API
のためにはそこまで有用なわけではありませ
ん。
Underscore
は、その関数のほとんどが
1
つ目の引数にコレクションを取るとい
う特性を活かして
_.chain
でチェーンを実装しています。対照的に、本書で定義して
いる関数は
1
つ目の引数に関数を取ります。これは部分適用とカリー化を容易にす
るために選択したものです。
メソッドチェーンには、様々な欠点が存在します。例えば、オブジェクトの
set
と
get
のロジックが堅く連結されてしまうこと（コマンドとクエリの分離（
Folwer
2010
））や、ぎこちないネーミングの問題などがあります。しかし、メソッドチェー
ンにおける一番大きな問題は、ひとつの呼び出しから次の呼び出しに移る際に、共通
の参照を変更してしまうということです（図
8-4
）。一方、関数型
API
は参照ではな
く値そのものを操作し、微妙に（時には大胆に）データを変換して新しい結果値を返
します。
図 8-4 チェーンされたメソッド呼び出しは共通の参照を変異させる
本節では、関数のパイプラインについて説明し、その効果的な使用法を紹介しま
す。理想的には、関数に渡されたオリジナルのデータは実行後もオリジナルのまま残
るべきです。関数型のコードにおけるチェーンは、期待されるデータ値が入力される
と、非破壊的変換を行い、そして新しいデータを返す動作が図 ...
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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.