结构的深度复制-如何?

要创建类实例的“deep”副本,您需要符合这些相关类的nscoping, Structs

import Foundation

struct Departure {
    var to: Stop
    var from: Stop

    init(from: Stop, to: Stop) {
        self.from = from
        self.to = to
    }
}

struct Stop {
    var name: String = ""

    init(named: String) {
        self.name = named
    }
}

class NearbyStopsViewModel: NSCopying {
    var stopViewModels: [StopViewModel]

    init(stops: [StopViewModel] = []) {
        self.stopViewModels = stops
    }

    func copy(with zone: NSZone? = nil) -> Any {

        var stops: [StopViewModel] = []
        self.stopViewModels.forEach { (stop) in
            stops.append(stop.copy() as! StopViewModel)
        }

        let nearbysvm = NearbyStopsViewModel.init(stops: stops)
        return nearbysvm

    }
}

class StopViewModel: NSCopying {

    var stop: Stop
    var name: String = ""
    var departures: [DepartureViewModel]

    init(stop: Stop, named: String, with departures: [DepartureViewModel] = [] ) {
        self.stop = stop
        self.name = named
        self.departures = departures
    }

    func copy(with zone: NSZone? = nil) -> Any {

        var departuresCopy: [DepartureViewModel] = []
        self.departures.forEach { (departure) in
            departuresCopy.append(departure.copy() as! DepartureViewModel)
        }

        let stopvm = StopViewModel.init(stop: self.stop, named: self.name, with: departuresCopy)
        return stopvm
    }
}


class DepartureViewModel: NSObject, NSCopying {

    var departure: Departure
    var name: String = ""

    init(name: String, departure: Departure) {
        self.name = name
        self.departure = departure
    }

    func copy(with zone: NSZone? = nil) -> Any {
        let departure = DepartureViewModel.init(name: self.name, departure: self.departure)
        return departure
    }
}


// Structs are passed by Value, making a 'minimal' copy of themselves as they move.
var pennStation = Stop(named: "Pennsylvania Station")
print(pennStation)
let copyByValue = pennStation
print(copyByValue) // "Pennsylvania Station"
pennStation.name = "Penn. Station"
print(copyByValue) // "Pennsylvania Station"

// Classes are passed by Reference
let clarkLake = Stop(named: "Clark and Lake")
let stateLake = Stop(named: "State and Lake")

let clarkToState = Departure(from: clarkLake, to: stateLake)

// DepartureViewModel is your lowest level class that conforms to NSCopying
let departure = DepartureViewModel(name: "clark to state", departure: clarkToState)
print(departure) // This Memory Address should never change.
let referenceDeparture = departure
departure.name = "Unexpected delay"
print(referenceDeparture.name)
print(referenceDeparture) // Same Address as departure.

let deepCopyOfDeparture = departure.copy() as! DepartureViewModel // Copy() and mutableCopy() will return a passed-by-value copy.
print(deepCopyOfDeparture) // Different Memory Address as departure


let stopvm = StopViewModel(stop: pennStation, named: "Penn. Station", with: [departure])
print("Stop View Model's Child Departure Instance(s): \(stopvm.departures)")
let copyOfSVM = stopvm.copy() as! StopViewModel
print("Copy of SVM Child Departure Instance(s): \(copyOfSVM.departures)")

输出:

车站(名称:“宾夕法尼亚站”)

车站(名称:“宾夕法尼亚站”)

<StackOverflow.DepartureViewModel:0x149dc4de0>

<StackOverflow.DepartureViewModel:0x149dc4de0>

<StackOverflow.DepartureViewModel:0x149da89a0>

<停止视图模型的子离开实例:<StackOverflow.Departure View Model:0x149dc4de0>

<SVM子出发实例副本:<StackOverflow.DepartureViewModel:0x149dc7630>

您可以利用默认情况下被深度复制的值类型,这里需要注意的是,所有成员也是值类型(结构、枚举、元组),并且这些成员只包含值类型,依此类推:

struct NearbyStopsViewModel {
    var stopViewModels: [StopViewModel]
}

struct StopViewModel {
    var stop: Stop
    var name: String
    var departures: [DepartureViewModel]?
}

struct DepartureViewModel: NSObject {
    var departure: Departure
    var name: String
}

struct Departure {
    // fields needed for the struct
}

不过,请注意,如果使用大量这些值(对于足够多的值来说,性能问题是不明显的),则可能会出现一些性能问题。