問題のある実装パターン 共通実装 以下のような applog パッケージ上のロガー実装を考えましょう。ここでは Go 標準の log.Logger をラップしていますが,様々な実装に拡張できることを想定しています。 package applog import ( "fmt" "log" "os" ) type Logger interface { Info(message string) Error(message string) } func NewLogger() Logger { return &logger{ inner: log.New(os.Stdout, "", log.LstdFlags), } } var _ Logger = (*logger)(nil) type logger struct { inner *log.Logger } func (l *logger)
![なぜ Go ではロガーをコンストラクタ DI してはならないのか](https://cdn-ak-scissors.b.st-hatena.com/image/square/7e22f053b8a233765fd3a3693055bf3807416a52/height=288;version=1;width=512/https%3A%2F%2Fres.cloudinary.com%2Fzenn%2Fimage%2Fupload%2Fs--7WXwHwZo--%2Fc_fit%252Cg_north_west%252Cl_text%3Anotosansjp-medium.otf_55%3A%2525E3%252581%2525AA%2525E3%252581%25259C%252520Go%252520%2525E3%252581%2525A7%2525E3%252581%2525AF%2525E3%252583%2525AD%2525E3%252582%2525AC%2525E3%252583%2525BC%2525E3%252582%252592%2525E3%252582%2525B3%2525E3%252583%2525B3%2525E3%252582%2525B9%2525E3%252583%252588%2525E3%252583%2525A9%2525E3%252582%2525AF%2525E3%252582%2525BF%252520DI%252520%2525E3%252581%252597%2525E3%252581%2525A6%2525E3%252581%2525AF%2525E3%252581%2525AA%2525E3%252582%252589%2525E3%252581%2525AA%2525E3%252581%252584%2525E3%252581%2525AE%2525E3%252581%25258B%252Cw_1010%252Cx_90%252Cy_100%2Fg_south_west%252Cl_text%3Anotosansjp-medium.otf_37%3Ampyw%252Cx_203%252Cy_121%2Fg_south_west%252Ch_90%252Cl_fetch%3AaHR0cHM6Ly9zdG9yYWdlLmdvb2dsZWFwaXMuY29tL3plbm4tdXNlci11cGxvYWQvYXZhdGFyLzk0ZWM3OGU4NDYuanBlZw%3D%3D%252Cr_max%252Cw_90%252Cx_87%252Cy_95%2Fv1627283836%2Fdefault%2Fog-base-w1200-v2.png)