Wrapper for UserDefaults with Codable in Swift 4

DefaultsStore.swift

import Foundation

final class DefaultsStore<Value: Codable> {

    private let defaults: UserDefaults

    private let encoder: PropertyListEncoder
    private let decoder: PropertyListDecoder

    private let key: String
    private let initialValue: Value

    var value: Value {
        didSet {
            permanentValue = value
        }
    }

    init(initialValue: Value, key: String = #function, defaults: UserDefaults = .standard, encoder: PropertyListEncoder = PropertyListEncoder(), decoder: PropertyListDecoder = PropertyListDecoder()) {
        self.key = key
        self.initialValue = initialValue
        self.value = initialValue
        self.defaults = defaults
        self.encoder = encoder
        self.decoder = decoder

        self.value = permanentValue
    }

    private var permanentValue: Value {
        get {
            if let data = defaults.data(forKey: key), let value = try? decoder.decode(Value.self, from: data) {
                return value
            }
            return initialValue
        }
        set {
            if let data = try? encoder.encode(newValue) {
                defaults.set(data, forKey: key)
            }
        }
    }
}