A brief recursive implementation of InsertionSort on generic Comparable element's arrays in Swift 4.

recursiveInsertionSort.swift

import Foundation

//InsertionSort

///Inserts a value into a sorted array
func insert<T: Comparable>(value: T,into array: [T]) -> [T] {
    
    guard let last = array.last else {
        
        return [value]
    }
    
    if value < last {
        
        return insert(value: value, into: Array(array.dropLast())) + [last]
    } else {
        return array + [value]
    }
}

//Sort an array using InsertionSort recursively.
func insertionSort<T: Comparable>(_ array: [T]) -> [T] {
    
    guard let last = array.last else {
        
        return []
    }
    
    return insert(value: last,into: insertionSort(Array(array.dropLast())))
}

let unsortedArray = [2,1,3,7,5,6,4,8,9]

let sorterArray = insertionSort(unsortedArray)