scala - 方法参数中多个连续的粗箭头在 Scala 中意味着什么？

Question

我知道一个方法可以有这样的代码:

def m(p1:Int => Int) ...

这意味着该方法采用返回 Int 的函数 p1

但是在浏览 Play! 时框架代码我发现了一个具有难以破译的方法的特征:

trait Secured {

  def username(request: RequestHeader) = request.session.get(Security.username)

  def onUnauthorized(request: RequestHeader) = Results.Redirect(routes.Auth.login)

  def withAuth(f: => String => Request[AnyContent] => Result) = {
    Security.Authenticated(username, onUnauthorized) { user =>
      Action(request => f(user)(request))
    }
  }

  /**
   * This method shows how you could wrap the withAuth method to also fetch your user
   * You will need to implement UserDAO.findOneByUsername
   */
  def withUser(f: User => Request[AnyContent] => Result) = withAuth { username => implicit request =>
    UserDAO.findOneByUsername(username).map { user =>
      f(user)(request)
    }.getOrElse(onUnauthorized(request))
  }
}

Play! Scala Security

f: User => Request[AnyContent] => Result 是什么意思？乍一看，它看起来像是一个返回 Request 类型的函数 r 的方法；然后，r 返回一个 Result。

这是正确的假设吗？

Answer 1

What does the f: User => Request[AnyContent] => Result mean? At first glance it looks like a method that returns a function r of type Request; r then returns a Result.

f 返回 Request[AnyContent] => Result 类型的函数，即采用 Request[AnyContent] 并返回的函数结果。

换句话说，f 是一个柯里化(Currying)函数。您可以将其称为 f(user)(request) 以获取 Result。