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SUMMARY OF “DI”
WHESON_LT #1 by @black_bracken
くろわらび
■ Twitter: @black_bracken
■ IN/B2
■ いろんな言語を触っている
■ いろんな趣味を浅く嗜んでいる
■ いろんなゲームを触っている
■ いろんな単位を落としている
■ https://bracken.black/
Ad: PicSorter
■ ← ダウンロード
■ 画像管理用のAndroid app
– Android 8.0以降で動く
■ ディレクトリ分けとか一時ファイルの
扱いで有用かも
■ ソースコード:
https://github.com/blackbracken/PicSorter
DIご存じですか?
DIとは
■ Dependency Injectionの略
– 直訳すると『依存性の注入』
■ デザインパターンの一種
– 簡単の為に今回はクラスベースOOP言語での利用を仮定します
■ 『制御の反転』によるオブジェクトの制御反転
– 制御というより管理に近い気もする
What is “dependency”?
■ (クラスなどからみて)利用するオブジェクトのこと
– 定数しかり他クラスのインスタンスしかり
– 振る舞いがオブジェクトに『依存』している
■ 依存性の注入は依存しているオブジェクトの外部からの注入ともいえる
Code: Not DI
Code: Constructor DI
DIの何が良いのか
■ 振る舞いと、依存の明記を分離出来る
■ コードが表す意味を正しく示しやすくなる
– 『車がエンジンを生み出す』と『車にエンジンを与える』
– どちらかといえば『制御の逆転』のメリットな気がする
■ 契約(インターフェース)さえあればそれに依存する機能の実装が可能に
– 実装を1つ1つ完了させなくて良い
– これはAPIとかでもよくある手法
■ テストがしやすくなる
– これは後述
DIとテスト
■ モック
– テスト用にダミーの値が入ったクラス
– これで依存しているオブジェクトにかかわらずユニットテストが行える
– ネットワークとかだと尚更
Code:Tested with DI
Code:Tester with DI
DIコンテナ
■ DIは外部から依存先を受け取られるようにする
– 即ちどこかから依存先を与える必要がある
■ そういうのを諸々管理して勝手に注入したりしてくれる
■ コードとか出したかったけど時間無さそうなのであきらめた
まとめ ■ DIはまあ言われれば当たり前のパターン
– 言語化したのがえらいと思います

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Summary of DI