Topological Sort in Swift

topologicalSort.swift

extension RelPath: Comparable {
    /// Sorts by lexicographical topological order.
    public static func < (_ a:RelPath, _ b:RelPath) -> Bool {
        let c = Swift.min(a.count, b.count)
        for i in 0..<c {
            if a[i] < b[i] { return true }
            if a[i] > b[i] { return false }
        }
        return a.count < b.count
    }
}