[英]Unwrap value of non-optional
var OpDoub:Optional<Double> = 1.23
func noopt(_ pp: Any) -> Any {
return pp
}
var p:Any = noopt(OpDoub)
print(p) // Optional(1.23)
print(p!) // error: cannot force unwrap value of non-optional type 'Any'
我可以在聲明 P 后得到 1.23 的值嗎? 我試過了:
var pp:Any? = p
print(pp) // Optional(Optional(1.23)) it turned out even worse :D
print(pp!) // Optional(1.23)
如果你想得到公正
1.23
...那么您應該將p
向下轉換為Double
:
var OpDoub:Optional<Double> = 1.23
func noopt(_ pp: Any) -> Any {
return pp
}
var p:Any = noopt(OpDoub)
if let doubleP = p as? Double { /// here!
print(doubleP) /// result: 1.23
}
編輯
如果你想解開p
(讓它不是可選的)並將它變成一個字符串,那么試試這個(基於這個很棒的答案):
func unwrap(_ instance: Any) -> Any {
let mirror = Mirror(reflecting: instance)
if mirror.displayStyle != .optional {
return instance
}
if mirror.children.count == 0 { return NSNull() }
let (_, some) = mirror.children.first!
return some
}
let unwrappedP = unwrap(p)
let string = "\(unwrappedP)" /// using String Interpolation https://docs.swift.org/swift-book/LanguageGuide/StringsAndCharacters.html#ID292
print("unwrapped string: \(string)")
結果:
解包字符串:1.23
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