我想将字符串中包含的字母的索引转换为整数值。尝试读取头文件,但找不到的类型Index,尽管它似乎符合ForwardIndexType使用方法的协议(例如distanceTo)。
Index
ForwardIndexType
distanceTo
var letters = "abcdefg" let index = letters.characters.indexOf("c")! // ERROR: Cannot invoke initializer for type 'Int' with an argument list of type '(String.CharacterView.Index)' let intValue = Int(index) // I want the integer value of the index (e.g. 2)
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编辑/更新:
Xcode 11•Swift 5.1或更高版本
extension StringProtocol { func distance(of element: Element) -> Int? { firstIndex(of: element)?.distance(in: self) } func distance<S: StringProtocol>(of string: S) -> Int? { range(of: string)?.lowerBound.distance(in: self) } }
extension Collection { func distance(to index: Index) -> Int { distance(from: startIndex, to: index) } }
extension String.Index { func distance<S: StringProtocol>(in string: S) -> Int { string.distance(to: self) } }
游乐场测试
let letters = "abcdefg" let char: Character = "c" if let distance = letters.distance(of: char) { print("character \(char) was found at position #\(distance)") // "character c was found at position #2\n" } else { print("character \(char) was not found") }
let string = "cde" if let distance = letters.distance(of: string) { print("string \(string) was found at position #\(distance)") // "string cde was found at position #2\n" } else { print("string \(string) was not found") }