swift - 希望从 `Any` 的 `valueForKeyPath` 值中清除此 switch 语句

Question

基本上我使用的是 KVC，并可能返回不同的值类型，并希望根据类型创建一个 switch 语句

我在这里尝试了答案，但它无法编译: Swift: Test class type in switch statement

        var value: String = "Unknown"
        switch node.value(forKeyPath: keyPath) {
        case let numberValue is NSNumber:
            if numberValue == 0 {
                value = "No"
            } else if numberValue == 1 {
                value = "Yes"
            }
        case let stringValue is String:
            value = stringValue
        default:
            break
        }

它说

"Pattern variable binding cannot appear in an expression"

和

"Cast from <> to unrelated 'NSNumber' always fails"

这里的代码对我有用:

        var value: String = "Unknown"
        let nodeValue = node.value(forKeyPath: keyPath)
        switch nodeValue {
        case is NSNumber:
            if let numberValue = nodeValue as? NSNumber {
                if numberValue == 0 {
                    value = "No"
                } else if numberValue == 1 {
                    value = "Yes"
                }
            }
        case is String:
            if let stringValue = nodeValue as? String {
                value = stringValue
            }
        default:
            break
        }

但我需要使用可选绑定(bind)来对新变量进行类型转换似乎有点不理想

有更好的方法吗？

Answer 1

有一种模式匹配和一次性转换的方法，我认为它实际上很干净:

switch nodeValue {
case let number as NSNumber:
    switch number {
    case 0: value = "No"
    case 1: value = "Yes"
    default: break
    }
case let string as String:
    value = string
default: break
}