objective c - Swift passing uninitialized object to block -

i have been trying figure out small thing quite easy objective c, not solve swift.

var loginviewcontroller: ssloginviewcontroller  let completion = {   loginviewcontroller.presentviewcontroller(ssfeedviewcontroller(), animated: true, completion: nil) }  loginviewcontroller = ssloginviewcontroller(completion: completion) 

the intention here pass ssloginviewcontroller completionblock present view controller. but, code above gives error.

variable 'loginviewcontroller' captured closure before being initialized.

delcaring uninitialized variable __block, objective c block take changed value within block.

it in objective c,

__block ssloginviewcontroller *loginviewcontroller; dispatch_block_t completion = ^ {   [loginviewcontroller presentviewcontroller:[[ssfeedviewcontroller alloc] init] animated: yes completion:nil] }; loginviewcontroller = [[ssloginviewcontroller alloc] initwithcompletion:completion]; 

how can similar behavior achieved swift ?

it should initialized nil (that's what's happening in objective-c code anyway; in objective-c arc, managed object pointers initialized nil if not otherwise initialized). means need optional. can use implicitly-unwrapped optional not have deal optional syntax since know it's going nil temporarily.

var loginviewcontroller: ssloginviewcontroller!  let completion = {   loginviewcontroller.presentviewcontroller(ssfeedviewcontroller(), animated: true, completion: nil) }  loginviewcontroller = ssloginviewcontroller(completion: completion) 

an additional problem, exists in objective-c code, there retain cycle. ssloginviewcontroller object stores , has strong reference completion block, , block has strong reference ssloginviewcontroller object. if know completion block exists while ssloginviewcontroller object alive, can have capture weak reference loginviewcontroller:

var loginviewcontroller: ssloginviewcontroller!  let completion = { [weak loginviewcontroller] in   loginviewcontroller.presentviewcontroller(ssfeedviewcontroller(), animated: true, completion: nil) }  loginviewcontroller = ssloginviewcontroller(completion: completion)