scala - 在 Scala 中使用运算符 orElse 的正确方法是什么？

Question

我想写两个服务，然后用orElse让两个服务组合在一起，即service_one或service_two。他们都是部分函数。

服务之一是:

val usersService = HttpService {
case request @ GET -> Root / "users" / IntVar(userId) =>
  Ok("test")
}

服务二是:

val versionService = HttpService{
  case req @ GET -> Root / "version" => {
    val jsonmap = ("origin" -> req.remoteAddr.getOrElse("unknown ip"))
    Ok(compact(render(jsonmap)))
   }
}

然后我想将它们组合在一起。

val service = userService orElse versionService   //the error happens here.

错误是:

[error] F:\workspace\frankcheckAPI\src\main\scala\com\cardaccess\ServiceApp.scala:46: value orElse is not a member of org.http4s.HttpService
[error]   val service = usersService orElse versionService
[error]                              ^
[error] one error found
[error] (compile:compileIncremental) Compilation failed

如何组合然后使然后的工作方式类似于如果大小写与第一个服务的路径匹配，则第一个服务工作，如果大小写与第二个服务的路径匹配。第二次服务工作。

ps:有关人士:

HttpService 对象的定义如下:

  type HttpService = Service[Request, Response]
  object HttpService {

/** Alternative application which lifts a partial function to an `HttpService`,
  * answering with a [[Response]] with status [[Status.NotFound]] for any requests
  * where the function is undefined.
  */
def apply(pf: PartialFunction[Request, Task[Response]], default: HttpService = empty): HttpService =
  Service.lift(req => pf.applyOrElse(req, default))
...
}

Answer 1

orElse 与 PartialFunction 一起使用，例如:

val t1: PartialFunction[Int, String] = {case 1 => "I am 1"}
val t2: PartialFunction[Int, String] = {case 2 => "I am 2"}
val t = t1 orElse t2
t(1)
> I am 1
t(2)
> I am 2

作为HttpService apply方法签名接受PartialFunction，我认为你可以这样做:

val usersService: PartialFunction[Request, Task[Response]] = {
  case request @ GET -> Root / "users" / IntVar(userId) =>
    Ok("test")
}

val versionService: PartialFunction[Request, Task[Response]] = {
  case req @ GET -> Root / "version" => {
    val jsonmap = ("origin" -> req.remoteAddr.getOrElse("unknown ip"))
    Ok(compact(render(jsonmap)))
   }
}
val service = HttpService {
  usersService orElse versionService
}