Convert CFString to NSString - Swift

Question

I\'m trying to write a program that will scan for available serial ports and present them in a popup menu. Why can I not take the CFString straight from the

Answer 1

At least as of Swift 2.0 (verify from a terminal with swift --version), you can convert a CFString to a native Swift String with a simple as String.

This is sufficient, since Swift's String type can be used anywhere NSString is expected.

An example with a kUTType* constant (kUTType* constants are defined by CoreServices and are CFStrings):

// Get UTF8 plain text from the pasteboard.
import AppKit
let str = NSPasteboard.generalPasteboard().stringForType(kUTTypeUTF8PlainText as String)

A more detailed example:

// Import at least the Foundation framework.
// Since Cocoa includes Foundation, `import Cocoa` works too.
// (Note that `import CoreServices`, even though it defines type `CFString`,
// is NOT enough - the conversion will fail.)
import Foundation

// Create a CFString.
// The fact that initializing from a `String` literal here works implies that
// the *reverse* cast - String -> CFString - also works.
var cfStr:CFString = "Cast me."

// Convert it to String.
var swiftStr = cfStr as String

---

To test what type you're dealing with:

cfStr is CFString // true
swiftStr is String // true

To get the string's type, use .dynamicType; in a string context, this reports the type name but note that you may get the name of a private internal class back:

"cfStr is a \(cfStr.dynamicType) instance."
// -> "cfStr is a _NSContiguousString instance." !!

Still, you can treat this as a CFString, as the is test above shows.

Use _stdlib_getDemangledTypeName() to get the true, underlying class name:

_stdlib_getDemangledTypeName(cfStr) // -> "ObjectC.CFString"
_stdlib_getDemangledTypeName(kUTTypeUTF8PlainText) // ditto

Answer 2

Swift.String and NSString are toll free bridged.

NSString and CFString can be cast to one another, but you can't directly cast from a Swift String to a CFString or vice versa.

Follow these steps to cast from a Core Foundation String to a Swift String:    

var cfStr:CFString = "Soon, I'll be a Swift String"
var nsTypeString = cfStr as NSString
var swiftString:String = nsTypeString

Example for CFTypeRef:

var cfStr:CFTypeRef = "Soon, I'll be a Swift String"
var nsTypeString = cfStr as NSString
var swiftString:String = nsTypeString

Answer 3

As for me, I like to make extentions and use them afterwards. It seems convenient and clear to read:

Extention:

extension CFString {
    var string: String {
        return self as String
    }
}

Usage:

let specificQueryPart: [String: NSObject] = [
            kSecReturnData.string: true as NSObject,
            kSecAttrService.string: key as NSObject,
            kSecMatchLimit.string: kSecMatchLimitOne
        ]