Generics ViewModel

genericsviewmodel.swift

//: Playground - noun: a place where people can play

import UIKit

protocol ViewModelType {
    associatedtype ViewType
    associatedtype ModelType

    var base: ModelType { get }
    var fields: [String: Any] { get set }
}

extension ViewModelType {
    func get<T>(key: String = #function, defaultValue: T) -> T {
        return (fields[key] as? T) ?? defaultValue
    }

    mutating func set<T>(key: String = #function, newValue: T) {
        fields[key] = newValue
    }
}

struct ViewModel<View, Model>: ViewModelType {
    typealias ViewType = View
    typealias ModelType = Model

    let base: Model
    var fields: [String: Any] = [:]

    init(_ base: Model) {
        self.base = base
    }
}

protocol ModelType {
    func at<V>(_ viewType: V.Type) -> ViewModel<V, Self>
}

extension ModelType {
    func at<V>(_ viewType: V.Type) -> ViewModel<V, Self> {
        return ViewModel(self)
    }
}

struct YourModel: ModelType {
    let text: String?
}

extension ViewModelType where ViewType: UITextView, ModelType == YourModel {
    var text: String {
        return base.text ?? ""
    }

    var hidden: Bool {
        set {
            set(newValue: newValue)
        }
        get {
            return get(defaultValue: false)
        }
    }
}
var vm = YourModel(text: "test").at(UITextView.self)
vm.text
vm.hidden