Scala, GUI and immutability

Question

I created an algorithm that calculates certain things. This can be considered as the model. The algorithm is implemented in a fully functional way, so it uses immutable classes only. Now using this model, I would like to develop a GUI layer on the top of it. However I do not know anything about the best-practises of building GUI in Scala. I intend to use ScalaFX.

My problem is the following: in ScalaFX (similarly to JavaFX) you can bind values from the GUI to object properties. This clearly violates the functional paradigm, but seems very convenient. This would require rewriting my classes to use bindable properties which would feel like the tail wagging the dog — the model would depend on the GUI.

On the other hand, I could have an independent GUI layer. In this case I would need proxy objects to bind to and I would have to create my model objects based on these proxy objects. This would feel more idiomatic but implies a lot of code duplication and extra work. My model and the proxy objects would have to be kept in sync and I would have to take care of copying the attributes.

What is a good way of doing this? A GUI is always full of mutability so functional programming does not feel right here. Nevertheless I love Scala so I would like to keep using it for the GUI, too.

Answer 1

Despite the extra effort, take the second approach. Create small mutable "view" instances for each of your model. Bind the views to the widgets and install observers or hooks that update the view proxies based on changes in your model. Don't let the GUI API dictate how your concurrency approach and model should look like.

I believe there are a few open source libraries around that provide a more functional and/or reactive abstraction layer to the plain Scala-Swing or Scala-FX.