GP was referring to the feature that getters/setters are invoked with property access. Swift's didSet/willSet distinction is unrelated to this feature. ES6 Java

GP was referring to the feature that getters/setters are invoked with property access. Swift's didSet/willSet distinction is unrelated to this feature. ES6 JavaScript, for instance, has this feature with just get/set methods. In Java (and JS) there's a separate, all-knowing garbage collector, while swift is reference counted. In an ARC runtime, the didSet/willSet distinction avoids explicit calls to release the object, which is pretty clearly a good thing on the programmer's end. You can debate whether the benefits of full garbage collectors outweigh their performance characteristics, but given ARC, the didSet/willSet distinction definitely makes sense.