[英]Defining new TYPE for partial function with an implicit parameters
我正在嘗試創建一個具有部分函數模式的新TYPE。 例:
新類型 :
type RouteFunc = (String, HttpServletRequest, HttpServletResponse) => Unit
用法 :
def myFunc(str:字符串,請求:HttpServletRequest,響應HttpServletResponse)myFunc(“”,Any,Any)
對於顯式傳遞的參數,這確實很好用,但是我想更改此類型定義,以便將HttpServletRequest, HttpServletResponse
隱式與顯式傳遞。
預期結果 :
def myFunc(str: String)(implicit request: HttpServletRequest, response HttpServletResponse)
我找不到一種方法來更改TYPE結構/定義以適應預期的模式,這是可能的還是語言的限制?
編輯 :
用法:
object Routes{
type RouteFunc = (String, HttpServletRequest, HttpServletResponse) => Unit
val routes = Map[String, RouteFunc](
"/data" -> DataSets.dashboard
)
def evaluateRoute()(implicit request: HttpServletRequest, response: HttpServletResponse) = {
val path = request.getPathInfo
val route = routes(path)
route(path, request, response)
}
}
object DataSets{
def dashboard(path: String, request: HttpServletRequest, response: HttpServletResponse) = {
response.setContentType("text/html")
response.setCharacterEncoding("UTF-8")
response.getWriter.write("Hello World")
}
}
我希望def dashboard
看起來像:
def dashboard(path: String)(implicit request: HttpServletRequest, response: HttpServletResponse)
編輯2 :
最后,我明確地傳遞了參數,因為對於@SergGr和@slouc所解釋的當前版本的Scala,這是不可能的:
import javax.servlet.http.{HttpServletRequest, HttpServletResponse}
import controllers.data._
import Routes._
class RoutingController() extends JettyHttpServlet {
type RouteFunc = (String, HttpServletRequest, HttpServletResponse) => Unit
type HttpRequest = String
type Path = String
val routes = Map[(String, HttpRequest), RouteFunc](
(GET, "/data") -> Data.dashboard,
(GET, "/assets/*") -> Assets.getAsset
)
override def Get()(implicit request: HttpServletRequest, response: HttpServletResponse): Unit = {
val path = request.getPathInfo
val pathTerms = path.split("/")
val getPaths = routes.filter(_._1._1 == request.getMethod.toUpperCase)
val filteredList = getPaths.flatMap{
route =>
if(route._1._2 == path){
Option(route)
}else {
val s = route._1._2.split("/")
if(route._1._2.startsWith("/assets")){
Option(route)
}else
None
}
}.toSeq
filteredList.head._2(path, request, response)
}
}
----------------------
import jetty.Routes
import jetty.Responses._
object Data {
import javax.servlet.http.{HttpServletRequest, HttpServletResponse}
def dashboard(path: String, eq: HttpServletRequest, qw: HttpServletResponse): Unit = {
implicit val s = eq
implicit val r = qw
Ok(Routes.html, views.html.data.dashboard.render("Dashboard").toString())
}
}
如果我的問題正確無誤,您想使用隱式參數定義一個函數。 這是不可能的。 它不僅是一種語言約束,而且還是一種邏輯約束。 函數是一個數學概念,那里沒有所謂的“隱式參數”。 無法提供參數的子集,而其余部分則“從作用域”中獲取。
在Scala中,有一種方法可以將方法轉換為函數。 有問題的機制稱為eta擴展。 給定一些方法fooMethod,則可以將對應的函數fooFunction定義為
def fooMethod(i: Input): Output
val fooFunction: Input => Output = (i: Input) => fooMethod(i)
// or
def fooMethod(i1: Input1, i2: Input2): Output
val fooFunction: Input1 => Input2 => Output = (i1: Input1) => (i: Input2) => fooMethod(i1, i2)
// or
def fooMethod(): Output
val fooFunction: Unit => Output = () => fooMethod()
如果您提供了需要函數的方法,則編譯器將自動執行eta擴展。 如果無法自動執行,則可以手動執行:
val fooFunction = fooMethod _
但是,由於前面提到的原因,如果您引入隱式參數,即使該技巧也失敗了。
例:
trait HttpServletRequest
trait HttpServletResponse
type RouteFunc = String => (HttpServletRequest, HttpServletResponse) => Unit
implicit val request = new HttpServletRequest {}
implicit val response = new HttpServletResponse {}
def myMethod1(str: String)(request: HttpServletRequest, response: HttpServletResponse) = println("1")
def myMethod2(str: String)(implicit request: HttpServletRequest, response: HttpServletResponse) = println("2")
val myFunc1: RouteFunc = myMethod1 _ // compiles fine
val myFunc2: RouteFunc = myMethod2 _ // nope
編輯:
鑒於您的編輯,這就是我的做法:
trait HttpServletRequest
trait HttpServletResponse
object Routes {
implicit val request = new HttpServletRequest {}
implicit val response = new HttpServletResponse {}
type RouteFunc = String => Unit
val routes = Map[String, RouteFunc]("/data" -> DataSets.dashboard())
}
object DataSets {
def dashboard()(implicit request: HttpServletRequest, response: HttpServletResponse): RouteFunc =
(path: String) => {
// impl of dashboard, uses request and response
}
}
您將路由定義為功能String => Unit
,並將儀表板定義為采用隱式請求和響應並為您構造路由的方法。
編輯2:
似乎在將來的Scala版本之一中將提供對帶有隱式參數的函數的支持。 我不喜歡這樣,我不會使用它,即使沒有它,我們在Scala中也會有太多隱含的地獄,但是很高興知道這一點,這樣我就不會一直聲稱這是不可能的:)
從Scala 2.12開始不支持隱式函數。 看起來當Dotty成為Scala的官方編譯器時,他們計划將其用於更高版本中的一個
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