Converting a string to a class in Swift - swift

Question

I am using Alamofire to make a GET request and am using the ObjectMapper library to convert the response into its own class in Swift.
Alamofire.request(self.REST_METHOD!, self.REQUEST_URL, headers : ["Authentication_Token" : authToken]).responseJSON { response in
if response.response != nil && response.response?.statusCode == 200 {
let json = JSON((response.result.value as? NSDictionary)!)
let classType : AnyObject.Type = NSClassFromString(entityType)! as AnyObject.Type
//let model = Mapper<classType>.map(json.rawString())
}
}
The entityType variable can be one of many types i.e. User, Student, Teacher, Staff, etc. I am trying to dynamically create a class type and create the model based on that.
However it crashes on the line let classType : AnyObject.Type = NSClassFromString(entityType)! as AnyObject.Type giving the error message:
fatal error: unexpectedly found nil while unwrapping an Optional value
Also when I uncomment the line let model = Mapper<classType>.map(json.rawString()), it gives me a compiler error:
classType is not a type
What is wrong with the above code

Answer 1

You're getting the error:
fatal error: unexpectedly found nil while unwrapping an Optional value
Because NSClassFromString is failing and returning nil, which then you are unwrapping, thereby causing the error.
I'm guessing that entityType contains a class name along the lines of myClass. Swift now uses namespaces, so to create a class from a string, the string must contain AppName.myClass.
You could either hardcode your app name, or use the following code to get it:
NSBundle.mainBundle().infoDictionary!["CFBundleName"] as! String
There are other problems with your code too. When NSClassFromString succeeds, it will create an instance of the class. This cannot be cast to a type. Also, you can't pass a variable as a generic in Mapper<classType>, as Swift needs to know the class type at compile time. Instead you could change the Mapper class to take the type as a parameter. For example:
Mapper.map(classInstance.dynamicType, json.rawString())
Although now that I re-read your question, you're using a library for Mapper, and are therefore probably reluctant to change it.
And looking at the doco for ObjectMapper, it needs you to create a Mapper instance - ie. instead of Mapper<MyClass>.map you need Mapper<MyClass>().map.