converting function in Objective-C to swift

Question

I'm trying to remove unescaped control character of a json, I could already converts it to String, but now I'm trying to adapt this function in Objective-C for swift.

- (NSString *)stringByRemovingControlCharacters: (NSString *)inputString 
{ 
NSCharacterSet *controlChars = [NSCharacterSet controlCharacterSet]; 
NSRange range = [inputString rangeOfCharacterFromSet:controlChars]; 
if (range.location != NSNotFound) { 
    NSMutableString *mutable = [NSMutableString stringWithString:inputString]; 
    while (range.location != NSNotFound) { 
        [mutable deleteCharactersInRange:range]; 
        range = [mutable rangeOfCharacterFromSet:controlChars]; 
    } 
    return mutable; 
} 
return inputString; 
} 

Following this as reference: Unescaped control characters in NSJSONSerialization

I got it but does not work:

func stringByRemovingControlCharacters(inputString: String) -> String {
var controlChars = NSCharacterSet.controlCharacterSet<NSObject>()
var range = inputString.rangeOfCharacterFromSet<NSObject>(controlChars)
if range.location != NSNotFound {
    var mutable = String = inputString
    while range.location != NSNotFound {
        mutable.deleteCharactersInRange(range)
        range = mutable.rangeOfCharacterFromSet<NSObject>(controlChars)
    }
    return mutable
}
return inputString
}

Cannot explicitly specialize a generic function

Cannot assign to immutable expression of type 'String.Type'

How could adapt it appropriately for swift (Swift 2.3)?

Answer 1

Objective-C translation (non-idiomatic)

The closest you can get to the code you provide is the following:

func stringByRemovingControlCharacters(string: String) -> String {
    let controlChars = NSCharacterSet.controlCharacterSet()
    var range = string.rangeOfCharacterFromSet(controlChars)
    var mutable = string
    while let removeRange = range {
        mutable.removeRange(removeRange)
        range = mutable.rangeOfCharacterFromSet(controlChars)
    }

    return mutable
}

Though I do not recommend you use the code above.

Swift 2.3

You can write it in a more Swifty way like this:

func stringByRemovingControlCharacters(string: String) -> String {
    return string.componentsSeparatedByCharactersInSet(.controlCharacterSet())
                 .joinWithSeparator("")
}

or even as an extension:

extension String {
    func stringByRemovingControlCharacters() -> String {
        return componentsSeparatedByCharactersInSet(.controlCharacterSet())
                   .joinWithSeparator("")
    }
}

For completion sake:

Swift 3.0

extension String {
    var removingControlCharacters: String {
        return components(separatedBy: .controlCharacters).joined()
    }
}