ios - Double exclamation !! mark in Swift? -

i know definition single exclamation mark, two?

i coding today , compiler "force" me add 1 more ! sentence:

mysignal.subscribenext({         (value: anyobject!) -> () in         let list: racsequence = value["myobject"]!!.rac_sequence         ... 

if use 1 ! mark, project doesn't compile, giving me error: "value of optional type 'anyobject?' not unwrapped; did mean use '!' or '?'?" add 1 more ! , works.

what's meaning two exclamation marks in swift?

you're storing anyobject! in dictionary, you're storing optional value. dictionary subscripts return optional of value you're storing, you're getting optional optional, why need 2 !, unwrap twice.