Scala隱式類依賴注入

Question

我想要一些幫助來整理這個場景。我有一個Akka actor，我想要注入一個依賴項，在這個例子中是RemoteFetcher，我也想在我的測試中模擬它。像這樣：

主/ src目錄/斯卡拉/ mypackage中/ Services.scala

package mypackage 
import RemoteFetcherFileSystem._ 

trait RemoteFetcher { 
    def fetch(path:String): Future[Stream[String]] 
} 

class MyRemoteResourceActor extends Actor with ActorLogging { 
    def fetchRemote(path:String) = implicitly[RemoteFetcher].fetch(path) 
    def receive = { 
    case FetchRemoteResource(path) => fetchRemote(path).map(_.foreach(sender ! _)) 
    } 
} 

對於這個工作我有我導入到上述文件的隱式對象。看起來是這樣的：

implicit object RemoteFetcherFileSystem extends RemoteFetcher { 
    def fetchRemote(path:String) = Future[Stream[String]] { ... reading from file system ... } 
} 

現在在我的測試中，我有來自akka-testkit的TestActor。在這裏，我想，而不是導入我的模擬依賴：

implicit object RemoteFetcherMock extends RemoteFetcher { 
    def fetchRemote(path:String) = Future[Stream[String]] { ... mock implementation ... } 
} 

我的問題是，編譯Services.scala我需要進口隱含對象。但是，我怎麼去在我的測試文件中覆蓋/覆蓋這個。我沒有使用隱式參數的原因是我想避免必須修改我所有的actor構造函數參數。

我環顧四周，閱讀了類型依賴注入模式，並根據教程讓它工作，但當我想在我的示例中進行測試和覆蓋時，我沒有得到它的工作。

Answer 1

我不知道如何與implicits做到這一點，但一般人能代替注入，像這樣：

trait RemoteFetcherComponent { 
    def remoteFetcher: RemoteFetcher 
    trait RemoteFetcher { 
    def fetch(path: String): Future[Stream[String]] 
    } 
} 

trait RemoteFetcherFileSystemComponent extends RemoteFetcherComponent { 
    val remoteFetcher = RemoteFetcherFileSystem 
    object RemoteFetcherFileSystem extends RemoteFetcher { 
    def fetch(path: String): Future[Stream[String]] = ??? 
    } 
} 

class MyRemoteResourceActor extends Actor with ActorLogging with RemoteFetcherFileSystemComponent { 
    def fetchRemote(path: String) = remoteFetcher.fetch(path) 
    def receive = { 
    case FetchRemoteResource(path) => fetchRemote(path).map(_.foreach(sender ! _)) 
    } 
} 

val myRemoteResourceActor = new MyRemoteResourceActor() 

然後測試值將被定義，像這樣：

trait RemoteFetcherMockComponent extends RemoteFetcherComponent { 
    def remoteFetcher = RemoteFetcherMock 
    object RemoteFetcherMock extends RemoteFetcher { 
    def fetch(path: String): Future[Stream[String]] = ??? 
    } 
} 

val myMockedResourceActor = new MyRemoteResourceActor with RemoteFetcherMockComponent { 
    override val remoteFetcher = super[RemoteFetcherMockComponent].remoteFetcher 
} 

你有一個問題的原因是因爲你使用它的方式與簡單地使用def fetchRemote(path: String) = RemoteFetcherFileSystem.fetch(path)沒有什麼不同。通過導入，您已經定義了實現，而不是稍後允許它被注入。

Answer 2

你也可以改變implicitly一個隱含參數：

trait RemoteFetcher { 
    def fetch(path: String): Future[Stream[String]] 
} 

object RemoteFetcher { 
    implicit val fetcher = RemoteFetcherFileSystem 
} 

class MyRemoteResourceActor extends Actor with ActorLogging { 
    def fetchRemote(path: String)(implicit remoteFetcher: RemoteFetcher) = remoteFetcher.fetch(path) 
    def receive = { 
    case FetchRemoteResource(path) => fetchRemote(path).map(_.foreach(sender ! _)) 
    } 
} 

然後，你可以通過導入RemoteFetcherMock重寫處於RemoteFetcher同伴對象解決了隱。有關隱式參數解析優先規則的更多信息，請參閱this post。