Swizzling uses the Objective-C runtime, which in turns handles the message passing mechanism. Unless you inherit from an NSObject, you can’t swizzle in Swift.
Unless you're building something on your own, in which case there is an (unoffically supported) attribute which you can use to opt-in to swizzling of methods. The difference being you have to opt-in, so you can't swizzle someone else's methods (unless they let you).