相关疑难解决方法(0)

如何在Scala中创建功能正常的可配置对象？我看过托尼莫里斯关于Readermonad 的视频,我仍然无法连接点.

我有一个硬编码的Client对象列表:

class Client(name : String, age : Int){ /* etc */}

object Client{
  //Horrible!
  val clients  = List(Client("Bob", 20), Client("Cindy", 30))
}

我希望Client.clients在运行时确定,可以灵活地从属性文件或数据库中读取它.在Java世界中,我定义了一个接口,实现了两种类型的源,并使用DI来分配一个类变量:

trait ConfigSource { 
  def clients : List[Client]
}

object ConfigFileSource extends ConfigSource {
  override def clients = buildClientsFromProperties(Properties("clients.properties"))  
  //...etc, read properties files 
}

object DatabaseSource extends ConfigSource { /* etc */ }

object Client {
  @Resource("configuration_source") 
  private var config : ConfigSource = _ //Inject it at runtime  

  val clients …

我正在尝试Reader monad用于依赖注入,但是当方法需要不同的依赖项时会遇到问题:

class PageFetcher {
  def fetch(url: String) = Reader((dep1: Dep1) => Try {
    ...
  })
}

class ImageExtractor {
  def extractImages(html: String) = Reader((deps: (Dep2, Dep3)) => {
    ...
  })
}


object MyImageFinder {
  def find(url: String) = Reader((deps: (PageFetcher, ImageExtractor)) => {
    val (pageFetcher, imageExtractor) = deps
    for {
      htmlTry <- pageFetcher.fetch(url)
      html <- htmlTry
      images <- imageExtractor.extractImages(html)
    } yield images
  })
}

// I add these 3 useless dependencies here just for demo
class Dep1 …