CODEWITHSUNDEEP
scalaplayframework
Daniel Wu
Daniel Wu

Reputation: 6003

Demystify example code from playframework (Security.scala)

In the file https://github.com/playframework/playframework/blob/master/framework/src/play/src/main/scala/play/api/mvc/Security.scala, it has the following example code in a comment:

 //in a Security trait                                                                    
 def username(request: RequestHeader) = request.session.get("email")                     
 def onUnauthorized(request: RequestHeader) = Results.Redirect(routes.Application.login)
 def isAuthenticated(f: => String => Request[AnyContent] => Result) = {
   Authenticated(username, onUnauthorized) { user =>
     Action(request => f(user)(request))
   }
}                                                                                       
//then in a controller                                                                   
def index = isAuthenticated { username => implicit request =>
    Ok("Hello " + username)
}

So I tried to write some similar code:

def test1(a: =>Int=>Int=>Int):String="1"
test1 {1 => 1 => 1} // But this line doesn't compile.

I called it the same way as isAuthenticated is called, so why doesn't my code compile?

Upvotes: 0

Views: 116

Answers (2)

wingedsubmariner
wingedsubmariner

Reputation: 13667

test1 {1 => 1 => 1} doesn't compile because {1 => 1 => 1} isn't a valid function definition. {x => y => 1}, on other hand, does compile. This is because 1 cannot be used as the name for a parameter.

Upvotes: 1

Michael Zajac
Michael Zajac

Reputation: 55569

Take a look at what happens when you paste def test1(a: =>Int=>Int=>Int):String="1" into the Scala REPL:

test1: (a: => Int => (Int => Int))String

test becomes defined as a function that accepts an another function as it's parameter. Notice the extra parenthesis in the REPL output. a is a function that maps Int to another function Int => Int.

So something like this would be more appropriate:

def a(i: Int): Int => Int = {j: Int => i + j}

test1(a)

Upvotes: 1

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