如何在 Swift 的泛型中声明基类？

Question

不起作用的代码示例，但我希望它能够成功编译。下面的源代码很好地描述了想法。您可以轻松地将其粘贴到 Swift Playground 中。

import UIKit

// MARK: - Base classes with generics

class FlowController {

}

class ViewModel<FlowControllerType: FlowController> {
    let flowController: FlowControllerType
    init (flowController: FlowControllerType) {
        self.flowController = flowController
    }
}

class ViewController<ViewModelType: ViewModel<FlowController>> {

    var viewModel: ViewModelType!
}

// MARK: - My implementation

class MyFlowController: FlowController {

}

class MyViewModel: ViewModel<MyFlowController> {
    override init (flowController: MyFlowController) {
        super.init(flowController: flowController)
    }
}

// ERROR: 'ViewController' requires that 'MyModelView' inherit from 'ViewModel<FlowController>'
class MyViewController: ViewController<MyViewModel> {

}

// MARK: - Code

let viewController = MyViewController()
viewController.viewModel = MyViewModel(flowController: MyFlowController())

问题是我想声明MyViewController，但出现错误：

'ViewController' requires that 'MyModelView' inherit from 'ViewModel<FlowController>'

问题是如何声明这些类以使其工作？我应该为此使用where 子句吗？我想在基类中拥有自己的 ViewController.viewModel 和 ViewModel.flowController 类型，以保持类之间的这些依赖关系。提前谢谢你。

相关问题： Swift generic inheritance

Answer 1

我可能已经回答了，但它看起来可能比这个解决方案更好。技巧在下面一行

class ViewController<FlowControllerType: FlowController, ViewModelType: ViewModel<FlowControllerType>> {

应该使用哪个来代替

class ViewController<ViewModelType: ViewModel<FlowController>> {

我希望其他人能做得更好，但目前只有这样有效。完整的游乐场示例：

import UIKit

// MARK: - Base classes with generics

class FlowController {

}

class ViewModel<FlowControllerType: FlowController> {
    let flowController: FlowControllerType
    init (flowController: FlowControllerType) {
        self.flowController = flowController
    }
}

class ViewController<FlowControllerType: FlowController, ViewModelType: ViewModel<FlowControllerType>> {

    var viewModel: ViewModelType!
}

// MARK: - My implementation

class MyFlowController: FlowController {

}

class MyViewModel: ViewModel<MyFlowController> {
    override init (flowController: MyFlowController) {
        super.init(flowController: flowController)
    }
}

class MyViewController: ViewController<MyFlowController, MyViewModel> {

}

// MARK: - Code

let viewController = MyViewController()
viewController.viewModel = MyViewModel(flowController: MyFlowController())