How to Add an Extension to Swift Array To Conditionally Append?

Question

Is there a way to do this as an extension to Array as opposed to a switch statement that's going to grow and grow?

    fileprivate var exteriorColorOptions = [ExteriorColorOption]()
    fileprivate var otherOptions = [SomeOtherOption]()
      : more options

    func add(option:FilteredOption) {

        switch(option) {
        case let thing as ExteriorColorOption:
                exteriorColorOptions.append(thing)
        case and on and on
        default:
            break
        }
    }

I would like to be able to just do the following with the right extension in place:

exteriorColorOptions.appendIfPossible(option)
otherOptions.appendIfPossible(option)

Note: switch approach came from Swift: Test class type in switch statement

Answer 1

This should work:

extension Array {

    mutating func appendIfPossible<T>(newElement: T) {
        if let e = newElement as? Element {
            append(e)
        }
    }
}

The conditional cast newElement as? Element succeeds if the new element conforms to or is an instance of (a subclass of) the arrays element type Element.

Example:

class A {}
class B: A {}
class C {}

var array: [A] = []

array.appendIfPossible(newElement: B())
print(array) // [B]

array.appendIfPossible(newElement: C())
print(array) // [B]