非通用 Swift class 可以实现 UIPickerViewDataSource 但通用版本不能

Question

Swift1.2/Xcode6.3.

为什么这是有效的：

class RangeDelegateNongeneric: NSObject, UIPickerViewDataSource {
    var values = [Int]()

    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return values.count
    }
}

但这不是：

class RangeDelegateGeneric<T>: NSObject, UIPickerViewDataSource {
    var values = [T]()

    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return values.count
    }
}

错误：Type RangeDelegateGeneric<T> does not conform to protocol UIPickerViewDataSource

更奇怪的是，Fix-it 消息：Candidate is not @objc, but protocol requires it 将 @objc 添加到每个函数的开头，但这并没有 Fix-it，而且 Fix-it 工具很高兴重复添加 @objc!

Answer 1

这在 Swift 2.0 中已修复，在 Xcode 7（撰写本文时为 beta 5）中经过专门测试。

99% 确定这个博客片段解释了它，尽管对编译器书呆子更友好的显式规范声明非常难以找到：

https://developer.apple.com/swift/blog/?id=29

[强调我的]

Swift-er SDKs: Swift 2 works even better with the Apple SDKs, thanks in part to two new features in Objective-C: nullability annotations and generics. The SDKs have been updated to annotate API that cannot return nil so you don’t need to use optionals as often. And with a true generics system employed by the SDKs you can more often preserve detailed type information in your Swift 2 code.

非通用 Swift class 可以实现 UIPickerViewDataSource 但通用版本不能

Non-generic Swift class can implement UIPickerViewDataSource but Generic version can't

generics

xcode

protocols

swift