I can\'t find a solution (here and on the web) for simply selecting/inserting/deleting stuff surrounded by dots (a common case in development) :
someobje
You might want to try this although it's not a proper answer:
put you cursor on s (after dot) and type: (which means visual until dot).
vf.
I believe the reason that you can't use vi. is dot is not something that vim could find its another pair like ( or ' ".