Engine-side callback when scriptObject field is set ?

Hey all.

so when i expose member fields to script via addField,
sometimes i'd like the object to get a callback when that field is touched by script.

for example,
i have an object with a "visibleDistance" parameter.
eg:

addField("visibleDist"       , TypeF32     , Offset(mVisibleDist       , Gui3DProjectionCtrl));

for efficiency, since i'm testing it every frame, i'd like to actually store and test against mVisibleDistSquared.

so i'd like to update mVisibleDistSquared whenever script updates mVisibleDist.

AFAIK, the only way to do this is with a setter/getter such as setVisibleDist().

- which is fine, i'm just curious if there's a mechanism i'm missing out on.

you know how i hate to miss out on mechanisms.

tia,
ooo

edit:
alternatively, the test could be this:

if (distSquared < mVisibleDist * mVisibleDist)

which would actually probably be totally fine in this example,
but if it were something more complicated might not be.

i guess i'm looking for implicit setter/getter action.