ios - What does ' !self ' means in Swift -

from this tutorial have seen kind of "!" + self operation, means in swift ?

override func animationdidstop(anim: caanimation!, finished flag: bool) {   self.transitioncontext?.completetransition(!self.transitioncontext!.transitionwascancelled())   self.transitioncontext?.viewcontrollerforkey(uitransitioncontextfromviewcontrollerkey)?.view.layer.mask = nil }   !self.transitioncontext!.transitionwascancelled()  //returns true self.transitioncontext!.transitionwascancelled()   // without ! , return false 

you can put (mental) bracket around it:

!(self.transitioncontext!.transitionwascancelled()) 

it means "logical not". if self.transitioncontext!.transitionwascancelled() = true, pass false function completetransition , vice-versa.

the ! in self.transitioncontext! optional unwrapping in swift , has nothing logic though.