swift - How do I turn an array of nullable items into a nullable array based on whether any of the items are null? -

i have array of nullable items may or may not have nils in it:

let source = [1, 2, 3] [int?] // or let source = [1, 2, nil] [int?] 

i want turn [int]? values ints if no items nil or nil if item nil.

what's idiomatic way this?

things i've tried:

// fails with: fatal error: can't unsafebitcast between types of different sizes  let result = source as? [int] 

and:

func tononnullable<t>(array: [t?]) -> [t]? {     if array.filter({$0 == nil}).count != 0 {         return nil;     }      return array.map({$0!})  }  // works, seems likey non-idiomatic (as being ineffecient).  let result = tononnullable(source) 

here's how write it:

let source = [1, 2, nil] [int?] var result : [int]? = {     in source {         if == nil {             return nil         }     }     return source.map {$0!} }() 

but doesn't meet "inefficient" consideration. has through array see if contains nil, nothing lost looping , doing that; inefficiency loop twice, because map loop. if hate that, here's way out:

var result : [int]? = {     var temp = [int]()     in source {         if let = {             temp.append(i)         } else {             return nil         }     }     return temp }() 

lots of idiomatic swifties in formulations, think!