Trying to create an array that automatically persists to a JSON file on disk

naïve_persisted_array.swift

import Foundation

public final class PersistedArray<T: Codable> {
    private var array: [T] {
        didSet {
            do {
                try save()
            } catch {
                print("\(error)")
            }
        }
    }

    private var url: URL = URL(string: "/dev/null")!

    var decoder: JSONDecoder = {
        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601
        return decoder
    }()

    var encoder: JSONEncoder = {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        return encoder
    }()

    //    public init(_ initial: [T] = []) {
    //        array = initial
    //    }

    public init(url: URL) {
        self.url = url
        array = []
        // try to load
        array = (try? load(from: url)) ?? []
    }

    public subscript(index: Int) -> T {
        get {
            return array[index]
        }
        set {
            array[index] = newValue
        }
    }

    public func get() -> [T] {
        return array
    }

//    public func append(_ element: T) {
//        array.append(element)
//    }

    private func load(from url: URL) throws -> [T] {
        if !FileManager.default.fileExists(atPath: url.path) {
            FileManager.default.createFile(atPath: url.path, contents: nil, attributes: nil)
        }
        let data = try NSData(contentsOf: url, options: .uncached)
        return try decoder.decode([T].self, from: data as Data)
    }

    private func save() throws {
        let data: NSData = try encoder.encode(array) as NSData
        try data.write(to: url, options: .atomic)
    }

    deinit {
        _ = try? save()
    }
}

extension PersistedArray: Collection {
    public func index(after i: Int) -> Int {
        return array.index(after: i)
    }

    public var startIndex: Int {
        return array.startIndex
    }

    public var endIndex: Int {
        return array.endIndex
    }
}

extension PersistedArray: RandomAccessCollection {}

extension PersistedArray: RangeReplaceableCollection {
    public convenience init() {
        self.init(url: URL(string: "/dev/null")!)
    }
}

var arr = PersistedArray<Int>(url: URL(string: "/dev/null")!)
arr.append(1)