protocol MyProtocol {}

extension MyProtocol {
    @discardableResult
    static func myFunction() -> Bool? {
        return true
    }
}

class ViewController {

    var myOptionalType: MyProtocol.Type?
    var myNonOptionalType: MyProtocol.Type!

    func test() {
        // warning: Expression of type 'Bool?' is unused
        myOptionalType?.myFunction()

        // no warning
        myNonOptionalType.myFunction()
    }

}