BinarySearch.swift

func binarySearch<Values>(_ value: Values.Element, in values: Values) -> Int? where Values: Collection, Values.Element: Comparable, Values.Index == Int {
    var values: Values.SubSequence = values[...]
    while !values.isEmpty {
        let midIndex = values.startIndex + (values.endIndex - values.startIndex) / 2
        let midValue = values[midIndex]
        if value < midValue {
            values = values[..<midIndex]
        } else if value > midValue {
            values = values[(midIndex + 1)...]
        } else {
            return midIndex
        }
    }
    return nil
}