gistfile1.txt

import UIKit

public class MyClass {
    
    private let instanceData:String = "yack"
    
    public typealias COMP_CALLBACK_FUNC = (param:String) ->(String)

    public func completionCallback( param:String, completionCallback: COMP_CALLBACK_FUNC )
    {
        completionCallback(param: param)
    }
    
}


let my = MyClass()

my.completionCallback("yack", completionCallback: { (param) -> (String) in
    
    let newString = "\(param)_YACK "
    
    println(newString)
    return newString
})

//you can also do it with a trailing closure
my.completionCallback("yack"){ (param) -> (String) in
    
    let newString = "\(param)_YACK "
    
    println(newString)
    return newString
}