From this Stackoverflow Question

Given this example method in Objective C:

- (void)addFilter:(GPUImageOutput <GPUImageInput>*)newFilter;

How to rewrite it in Swift, saying that the input parameter is of Class GPUImageOutput (or subclass), and, at the same time, conforms to the protocol GPUImageInput ?

In Swift, the solution comes from Generics:

Given these example declarations of protocol, main class and subclass:

protocol ExampleProtocol {
    func printTest() // classes that implements this protocol must have this method
 }

// an empty test class
class ATestClass
{
}

// a child class that implements the protocol
 class ATestClassChild : ATestClass, ExampleProtocol
 {
     func printTest()
     {
         println("hello")
     }
 }

Now, you want to define a method that takes an input parameters of type ATestClass (or a child) that conforms to the protocol ExampleProtocol. Write the method declaration like this:

func addFilter<T where T: ATestClass, T: ExampleProtocol>(newFilter: T)
{
    println(newFilter)
}

The original method, redefined in Swift, should be

func addFilter<T where T:GPUImageOutput, T:GPUImageInput>(newFilter:T!)
{
    // ...
}