Change typed refs in VmBindings to getset

[marner2]

This PR is very similar to #459 in that we take a ref field and convert it to a getter and a setter that has a mutable backing value. This allows us to box/unbox it.

This will conflict with #511 because of it renaming 'value to 't. It's an easy resolution.

[TysonMN]

This allows us to box/unbox it.

This seems possible to me.

Can you be more specific about what doesn't work?

[marner2]

@TysonMN you can't box/unbox a ref value because in doing so, you will create a "new" ref which won't be set if anyone with the "old" ref assigns to it. There's no way to put something "between" a ref set and it assigning the value. However with get/set functions we can easily do this.

[TysonMN]

@TysonMN you can't box/unbox a ref value because in doing so, you will create a "new" ref which won't be set if anyone with the "old" ref assigns to it. There's no way to put something "between" a ref set and it assigning the value. However with get/set functions we can easily do this.

Yes. And I was thinking that would be ok; that there isn't anywhere that would have a reference to the old ref.

Even so, I like your change. I think using functions is more convincingly correct.