For those wishing Java had a similar feature, there's Manifold: https://github.com/manifold-systems/manifold/tree/master/man...

Manifold is a very interesting project that adds a lot of useful features to Java (operator overloading, extension classes, and a whole bunch more). I don't know if it's smart to use it in production code because you basically go from writing Java to writing Manifold, but I still think it's a fun project to experiment with.