Swift Array.map closure issue - arrays

Question

I want to improve on a closure I wrote using Swift's Array.map function
I'm basically taking an Array and remapping all of its elements using a closure.
// Here's the array:
var numbersArray = [1, 2, 3, 4, 5]
// Here's the closure - it takes whatever number is passed into it and
// multiplies it by 2.0
var multiplier = { (currentNum: Int) -> Double in
let result = Double(currentNum) * 2.0
return result
}
// And here's how I'm calling it:
var newArray = numbersArray.map(multiplier)
And this works perfectly.
But what if I want to multiply everything by 2.1? or 3.5? or any value? In other words, what if I want to make the amount I multiply by also be a variable? And have it be passed into the closure as a second argument?
I tried adding it to the argument list like this:
var multiplier = { (currentNum: Int, factor: Double) -> Double in
let result = Double(currentNum) * factor
return result
}
and then changing my call to this:
var newArray = numbersArray.map(multiplier, 3.5)
but I'm getting all sorts of errors (and I tried all sorts of variations on this of course.)
What am I doing wrong?

Answer 1

Edit: Note: This language feature was removed in Swift 2.
A swift-er way than connor's answer (but along the same lines), is to use a curried function. From The Swift Programming Language->Language Reference->Declarations->Curried Functions and Methods:
A function declared this way is understood as a function whose return
type is another function.
So you can simplify this:
func multiplier(factor: Double) -> (Int)->Double
{
return { (currentNum: Int) -> Double in
let result = Double(currentNum) * factor
return result
}
}
to this:
func multiplier(factor: Double)(currentNum: Int) -> Double {
return Double(currentNum) * factor
}
and use it exactly the same way:
let numbersArray = [1, 2, 3, 4, 5]
let multipliedArray = numbersArray.map(multiplier(3.5))

Answer 2

You can use a higher order function to produce a custom function that you can then use with the array's map function. Like this:
var numbersArray = [1, 2, 3, 4, 5]
func multiplier(factor: Double) -> (Int)->Double
{
return { (currentNum: Int) -> Double in
let result = Double(currentNum) * factor
return result
}
}
var newArray = numbersArray.map(multiplier(2.5))