在单个 Switch 语句中进行模式匹配和条件绑定 [英] Pattern match and conditionally bind in a single Switch statement

问题描述

有没有办法把这个if/else if/else阶梯写成switch语句?

Is there a way to write this if/else if/else ladder as a switch statement?

let x: Any = "123"

if let s = x as? String {
    useString(s)
}
else if let i = x as? Int {
    useInt(i)
}
else if let b = x as? Bool {
    useBool(b)
}
else {
    fatalError()
}

这是我的尝试:

switch x {
case let s where s is String:   useString(s)
case let i where i is Int:      useInt(i)
case let b where b is Bool:     useBool(b)
default: fatalError()
}

它成功地选择了正确的路径，但是s/i/b仍然是Any类型.is 检查对转换它们没有任何影响.这迫使我在使用前强制使用 as! 进行强制转换.

It successfully chooses the right path, but s/i/b are still of type Any. The is check doesn't have any effect in casting them. This forces me to force cast with as! before usage.

有没有办法在一个 switch 语句中打开类型，并将其绑定到一个名称?

Is there a way to switch on the type, and bind it to a name, all in one switch statement?

推荐答案

当然，您可以使用 条件转换模式 case let x as Type:

Sure, you can use the conditional casting pattern case let x as Type:

let x: Any = "123"

switch x {
case let s as String:
    print(s)   //use s
case let i as Int:
    print(i)   //use i
case let b as Bool:
    print(b)   //use b
default:
    fatalError()
}

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