[Request for Comments] Behavior / InputMap

[Michael Strauß]

> Yes, one of the features the new design provides is ability to modify key mappings by the user at runtime.  So yes, not only it needs to be mutable, but it also adds some APIs for exactly that.
>

I struggle to see a use case for this feature. I can imagine that
there might be some use cases that call for customized input mappings,
but why would this translate to a _mutable_ input map? That's quite a
departure from the way other parts of JavaFX work.

For example, skins are also immutable. If you want to have a different
skin for a control, you don't somehow modify the existing skin
instance; instead, you'd create a new skin class (or -- somehow --
extend an existing skin class), and then install that new skin on your
control.

An input map shouldn't bind input events directly to instance methods
of a particular control instance. It should define the mapping of
events to methods symbolically:

Instead of mapping Event => instance.method(), it should map Event =>
Control::method. The input map could then be stateless and immutable,
and can be set on any control instance. If you want to change the
mappings, just set a different input map instance. There's no need
that an input map would retain a reference to any particular control,
since the control reference can be passed into the input map just as
easily.