If a Swift class is made available to Objective-C code (using the @objc annotation, or subclassing an Objective-C class), that class will use message sends for

If a Swift class is made available to Objective-C code (using the @objc annotation, or subclassing an Objective-C class), that class will use message sends for calling methods. Using an Objective-C class, or a @objc Swift class, from Swift will also use message sends for method calls.