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。它们都是偏函数。

服务一是：

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)))
   }
}

然后我想把它们结合在一起。

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 then make then 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。第二项服务工作。

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 一起使用PartialFunction，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HttpServiceapply 方法签名accept 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
}