Abstract functions in Swift Language

I'd like to create an abstract function in swift language. Is it possible?

class BaseClass {
    func abstractFunction() {
        // How do I force this function to be overridden?
    }
}

class SubClass : BaseClass {
    override func abstractFunction() {
        // Override
    }
}

There no concept of abstract in Swift (like Objective-C) but you can do this :

class BaseClass {
    func abstractFunction() {
        preconditionFailure("This method must be overridden") 
    } 
}

class SubClass : BaseClass {
     override func abstractFunction() {
         // Override
     } 
}

What you want is not a base class, but a protocol.

protocol MyProtocol {
    func abstractFunction()
}

class MyClass : MyProtocol {
    func abstractFunction() {
    }
}

If you don't supply abstractFunction in your class it's an error.

If you still need the baseclass for other behaviour, you can do this:

class MyClass : BaseClass, MyProtocol {
    func abstractFunction() {
    }
}