Swift 协议继承和协议一致性问题

问题描述

protocol BasePresenterProtocol : class {}
protocol DashboardPresenterProtocol : BasePresenterProtocol {}

final class DashboardPresenter {
    weak var view: DashboardPresenterProtocol?

    init() {
        self.view = DashboardViewController()
    }

    func test() {
        print("Hello")
    }
}

extension DashboardPresenter: DashboardViewProtocol { }

protocol BaseViewProtocol : class {
    weak var view: BasePresenterProtocol? { get set }
}

protocol DashboardViewProtocol : BaseViewProtocol {
}

class DashboardViewController {
}

extension DashboardViewController: DashboardPresenterProtocol { }

在上面的代码中，我在下面一行出现错误

In the above code, I get an error at following line

extension DashboardPresenter: DashboardViewProtocol { }

那个，DashboardPresenter 不确认协议 DashboardViewProtocol，但我在 DashboardPresenter 中声明了 weak var view: DashboardPresenterProtocol? .虽然我已经声明

that, DashboardPresenter doesn't confirm to protocol DashboardViewProtocol, but I have declared weak var view: DashboardPresenterProtocol? in DashboardPresenter . Although I have declared

为什么我会收到这个错误?请让我知道我在这段代码中做错了什么.

Why am I getting this error ? Please let me know what I am doing wrong in this code.

推荐答案

您不能使用 DashboardPresenterProtocol 类型的属性实现 BasePresenterProtocol? 类型的读写属性要求?>.

You cannot implement a read-write property requirement of type BasePresenterProtocol? with a property of type DashboardPresenterProtocol?.

考虑一下如果这可能会发生什么，并且您将 DashboardPresenter 的实例向上转换为 DashboardViewProtocol.您可以将任何符合 BasePresenterProtocol 的内容分配给 DashboardPresenterProtocol? 类型的属性——这将是非法的.

Consider what would happen if this were possible, and you upcast an instance of DashboardPresenter to DashboardViewProtocol. You would be able to assign anything that conforms to BasePresenterProtocol to a property of type DashboardPresenterProtocol? – which would be illegal.

出于这个原因，读写属性要求必须保持不变(尽管值得注意的是，只读属性要求应该能够协变——但目前不支持).

For this reason, a read-write property requirement has to be invariant (although it's worth noting that a readable-only property requirement should be able to be covariant – but this currently isn't supported).

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