It seems that this kind of thing comes up every so often when users are creating custom controls. I know I’ve rolled my own Attachment classes a few times for my own custom controls. I usually start with either the Button or Slider Attachment class, copy it, and hack away until it fits my use case.
Based on that, I’m wondering if JUCE shouldn’t have an abstract Attachment class so we could be a bit more proper and safe when attaching our own custom controls.