このコードをmacOSで実行すると、stringUTF16Backendを使うとtest()内でクラッシュする。 import Foundation #if !compiler(>=5) private extension String.UTF8View { func withContiguousStorageIfAvailable<R>(_ body: (UnsafeBufferPointer<Element>) throws -> R) rethrows -> R? { return nil } } #endif extension String { var nativeEncoding: Encoding { return utf8.withContiguousStorageIfAvailable({$0}) != nil ? .utf8 : .utf16 } } func printUTF16<S: StringProtocol>(_ string: S, label: String) { print(label, string.utf16.map { "\\u{\(String($0, radix: 16))}" }.joined()) } func test(_ string: String) { let utf16Index = string.utf16.index(before: string.utf16.endIndex) let utf16Before = string[..<utf16Index] printUTF16(utf16Before, label: "before:") let utf16After = string[utf16Index...] printUTF16(utf16After, label: "after:") printUTF16(utf16Before + utf16After, label: "joined:") print(utf16After.utf8.count) print(utf16After.utf16.count) } // https://emojipedia.org/family-man-woman-girl-boy/ let string = "\u{1f468}\u{200d}\u{1f469}\u{200d}\u{1f467}\u{200d}\u{1f466}" print(string.nativeEncoding) test(string) let tempfileURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(UUID().uuidString) try string.write(to: tempfileURL, atomically: true, encoding: .utf16) let stringUTF16Backend = try String(contentsOfFile: tempfileURL.path) print(stringUTF16Backend.nativeEncoding) test(stringUTF16Backend) defer { try! FileManager.default.removeItem(at: tempfileURL) } (edited)
