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IIUC refinements are module-local so they are modular and don't break anything.

module-local as in, creating a new type that can't be exchanged with the outside? Or converting the value's type on the fly when it gets passed somewhere else? I doubt either would be very usable.

Edit: the page refers to open classes, and I think the idea is that you can redefine methods on Object and have it apply to every object.

my understanding is that the method call is statically dispatched, and the dispatch is tweaked per module.

So, if I pass a String to your api and you invoke method X it will invoke the one redefined in your module, while outside it stays the same (more like scala implicits than ruby's open classes).

EDIT:

to clarify how I understand this: the authors have basically decided that the module is the element of behavior specialization, and method calls are basically static functions with syntax sugar, and a class is only a data container with some default implementations for the functions.

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