我想扩展一个Dictionary的方法,但只有当Key是String类型时.
我试着这样做：
extension Dictionary where Key: String {
mutating func lowercaseKeys() {
for key in self.keys {
self[key.lowercase] = self.removeValueForKey(key)
}
}
}
并得到错误：
Type ‘Key’ constrained to non-protocol type ‘String’
基于这个错误信息,我可以告诉我只能用协议进行这种过滤…有没有办法绕过这个？
我相信最符合您需求的协议是StringLiteralConvertible,其中有几个额外的行将让您完成此操作
原文链接：https://www.f2er.com/swift/319641.htmlextension Dictionary where Key: StringLiteralConvertible {
mutating func setAllKeysLowercase() {
for key in self.keys {
if let lowercaseKey = String(key).lowercaseString as? Key {
self[lowercaseKey] = self.removeValueForKey(key)
}
}
}
}
var stringKeyDictionary = [ "Hello" : NSObject(),"World" : NSObject() ]
stringKeyDictionary.setAllKeysLowercase()
print( stringKeyDictionary )
// Prints: ["hello": <NSObject: 0x1007033c0>,"world": <NSObject: 0x1007033d0>]
var numberKeyDictionary = [ 0 : NSObject(),1: NSObject() ]
numberKeyDictionary.setAllKeysLowercase() //< Won't compile,keys are not strings
