Iterative binary search

BinarySearch.swift

extension RandomAccessCollection where Element: Comparable {
    func binarySearch(target: Element) -> Index? {
        guard !isEmpty else {
            return nil
        }
        
        var start = startIndex
        var end = endIndex
        
        while start <= end {
            let half = distance(from: start, to: end) / 2
            let middleIndex = index(start, offsetBy: half)
            
            let middleValue = self[middleIndex]
            
            if middleValue == target {
                return middleIndex
            } else if target < middleValue {
                end = index(before: middleIndex)
            } else {
                start = index(after: middleIndex)
            }
        }
        
        return nil
    }
}