Easy API to store individual entries in UserDefaults to speed up access in large applications.

samples.swift

extension MyCoordinator: StorableItemOptional {
    static let storageDB = Storage.Database<ItemType?>(table: storageTable) { storageInitializer() }
    static let storageTable = Storage.Table(name: "IDENTIFIER")
    static var storageInitializer: () -> ItemType? {
        { nil }
    }

    
}


extension MyCoordinator: StorableItem {
    static let storageDB = Storage.Database<ItemType>(table: storageTable) { storageInitializer() }
    static let storageTable = Storage.Table(name: "IDENTIFIER")
    static var storageInitializer: () -> ItemType {
        { ItemType() }
    }

}

////

extension MyCoordinator {
    func storeDatabase() {
        Self.storageDB.store(item: itemInstance)
    }

    func restoreDatabase() {
        itemInstance = Self.storageDB.restore()
    }
}

StorageDB.swift

//
//  Storage.swift
//  MaxwellSpex
//
//  Created by mark maxwell on 5/13/20.
//  Copyright © 2020 maxwell.design. All rights reserved.
//

import Combine
import Foundation

protocol StorableItemOptional {
    associatedtype Item: Codable
    static var storageDB: Storage.Database<Item?> { get }
    static var storageTable: Storage.Table { get }
    static var storageInitializer: () -> Item? { get }
}

protocol StorableItem {
    associatedtype Item: Codable
    static var storageDB: Storage.Database<Item> { get }
    static var storageTable: Storage.Table { get }
    static var storageInitializer: () -> Item { get }
}

class Storage: ObservableObject {
    static let globalKeyspace = "com.maxwelldesign.v1"
   
    class Database<Item: Codable> {
        var keyspace: String
        let model: TableModel
        let builder: () -> Item

        let queue = DispatchQueue(label: "save.\(UUID().uuidString)")
        let lock = NSLock()

        var observer: AnyCancellable?

        init(keyspace: String = Storage.globalKeyspace, table: Table, initializer: @escaping () -> Item) {
            self.keyspace = keyspace
            model = Storage.table(for: table)
            builder = initializer
            loadInitialData()
            setupObserver()
        }

        func loadInitialData() {
            model.table.data = storage.string(forKey: tableKeyspace)
        }

        func setupObserver() {
            observer = model
                .objectWillChange
                .throttle(for: .milliseconds(model.table.delayMS), scheduler: RunLoop.main, latest: true)
                .sink(receiveValue: { [weak self] _ in
                    self?.persist()
                })
        }

        func store(item: Item) {
            model.table.data = item.asJSONString()
        }

        var storage: UserDefaults {
            UserDefaults.standard
        }

        var tableKeyspace: String {
            "\(keyspace).\(model.table.name)"
        }

        func restore() -> Item {
            if let stored = model.table.data ?? storage.string(forKey: tableKeyspace) {
                return Codec.object(fromJSON: stored) ?? builder()
            }
            return builder()
        }

        func persist() {
            performInQueue {
                guard let data = model.table.data else { return }
                self.storage.set(data, forKey: tableKeyspace)
            }
        }

        func performInQueue(_ closure: () -> Void) {
            queue.sync {
                lock.lock()
                closure()
                lock.unlock()
            }
        }
    }

    class TableModel: ObservableObject {
        @Published var table: Table
        init(table: Table) {
            self.table = table
        }
    }

    struct Table {
        var name: String
        var data: String?
        var delayMS = 250
    }
}

extension Storage {
    @Atomic static var tables: [String: TableModel] = [:]

    static func table(for table: Storage.Table) -> TableModel {
        var t = tables
        defer {
            tables = t
        }
        let result = t[table.name] ?? TableModel(table: table)
        t[table.name] = result
        return result
    }
}