Example of using ranges with arrays in Swift 4

FunWithRanges.swift

import Foundation

/// https://developer.apple.com/documentation/swift/range

enum NamedService: String {
    case altamontCorridor
    case californiaZephyr
    case caltrain
    case capitolCorridor
    case coaster
    case coastDaylight
    case coastStarlight
    case metrolink
    case napaValley
    case pacificSurfliner
    case sanJoaquins
    case skunkTrain
    case sonomaMarin
    case sprinter

    static let all: [NamedService] = [
        .altamontCorridor,
        .californiaZephyr,
        .caltrain,
        .capitolCorridor,
        .coaster,
        .coastDaylight,
        .coastStarlight,
        .metrolink,
        .napaValley,
        .pacificSurfliner,
        .sanJoaquins,
        .skunkTrain,
        .sonomaMarin,
        .sprinter,
    ]
}

let startIndex = NamedService.all.startIndex
let endIndex = NamedService.all.endIndex

guard let coasterIndex = NamedService.all.index(of: .coaster) else {
    fatalError("couldn't find index for .coaster")
}

let afterCoasterIndex = coasterIndex.advanced(by: 1)

NamedService.all[startIndex...coasterIndex]
/* altamontCorridor
 * californiaZephyr
 * caltrain
 * capitolCorridor
 * coaster
 */

NamedService.all[afterCoasterIndex..<endIndex]
/*
 * coastDaylight
 * coastStarlight
 * metrolink
 * napaValley
 * pacificSurfliner
 * sanJoaquins
 * skunkTrain
 * sonomaMarin
 * sprinter
 */