Swift 3 - Function for Wrapping an Array - arrays

Question

As I try to learn Swift 3, I am attempting to "Wrap an Array of Elements". In Swift 3 Playgrounds, I was able to implement code that wraps an array. My problem occurs when I try to create a function that implements my code.
If you take the following code and copy-paste it to a Swift 3 Playground then you will likely see what I am trying to do. Change the selectedElement and on the right you will see the correct newArray. You can interchange the different elements for the selectedElement and the newArray will change accordingly.
I noted one of my failed attempts at turning this into a function.
import UIKit
let myArray = ["a", "b", "c", "d", "e"]
let selectedElement = "a"
//func arrayWrapper(inputArray: Array<String>) -> Array<String> {
var oldArray = [String]()
var priorElements = [String]()
var newArray = [String]()
for element in myArray {
if element == selectedElement || oldArray.count > 0 {
oldArray.append(element)
} else {
priorElements.append(element)
}
newArray = oldArray + priorElements
}
//return newArray
//}
priorElements
oldArray
oldArray + priorElements
newArray

Answer 1

Your method works fine.
The only problem I see is that you are trying to access the variables created inside the function outside of the function scope.
//priorElements
//oldArray
//
//oldArray + priorElements
arrayWrapper(inputArray: myArray)

Answer 2

Well, your non-function solution to this problem takes two inputs - the array you want to wrap, and the element you want it to wrap at. Therefore, your function should have two parameters as well:
// note the second parameter
func arrayWrapper(inputArray: Array<String>, selectedElemented: String) -> Array<String> {
var oldArray = [String]()
var priorElements = [String]()
var newArray = [String]()
for element in myArray {
if element == selectedElement || oldArray.count > 0 {
oldArray.append(element)
} else {
priorElements.append(element)
}
newArray = oldArray + priorElements
}
return newArray
}
Here is a more general version of this function, as an extension of Array:
extension Array where Element : Equatable {
func wrap(around selectedElement: Element) -> Array<Element> {
var oldArray = [Element]()
var priorElements = [Element]()
var newArray = [Element]()
for element in self {
if element == selectedElement || oldArray.count > 0 {
oldArray.append(element)
} else {
priorElements.append(element)
}
newArray = oldArray + priorElements
}
return newArray
}
}
// usage
myArray.wrap(around: selectedElement)