An implementation of Merge Sort in Swift

MergeSort.swift

func mergeSort(numbers: Int[], left: Int, right: Int) {
    if right > left {
        let splitIndex = (left + right) / 2
        mergeSort(numbers, left, splitIndex)
        mergeSort(numbers, splitIndex+1, right)
        
        var result = Int[]()
        var nextLeft = left
        var nextRight = splitIndex + 1
        
        while nextLeft <= splitIndex && nextRight <= right {
            if numbers[nextLeft] < numbers[nextRight] {
                result.append(numbers[nextLeft])
                nextLeft++
            }
            else {
                result.append(numbers[nextRight])
                nextRight++
            }
        }
        
        for i in nextLeft...splitIndex {
            result.append(numbers[i])
        }
        
        for i in nextRight...right {
            result.append(numbers[i])
        }
        
        for i in 0..result.count {
            numbers[left + i] = result[i]
        }
    }
}