This is a simple merge sort without optimizations written in the new Swift language for IOS

Merge Sort in Swift (IOS)

func mergeSort(arr: [Int]) -> [Int]{
    
    func merge(left: [Int], right: [Int]) -> [Int] {
        
        var m = 0
        var merged : [Int] = []
        
        var i = 0, j=0
        
        while i < left.count && j < right.count {
            merged.insert(
                left[i] < right[j] ? left[i++] : right[j++], atIndex: m++
            )
        }
        
        while i < left.count {
            merged.insert(left[i++], atIndex: m++)
        }
        
        while j < right.count {
            merged.insert(right[j++], atIndex: m++)
        }
        
        return merged
    } // end merge()
    
    
    if arr.count <= 1 {
        return arr
    }
    
    let middle  = Int( floor((Double(arr.count)/2)))
    
    let left = mergeSort(Array(arr[0..<middle]))
    
    let right = mergeSort(Array(arr[middle..<arr.count]))
    
    return merge(left, right)
}