swift : Closure declaration as like block declaration

Question

We can declare block as below in Objective-C.

typedef void (^CompletionBlock) (NSString* completionReason);

I\'m trying to do this in swift

Answer 1

The syntax for function types is (in) -> out.

typealias CompletionBlock = (NSString?) -> Void
// or
typealias CompletionBlock = (result: NSData?, error: NSError?) -> Void

var completion: CompletionBlock = { reason in print(reason) }
var completion: CompletionBlock = { result, error in print(error) }

Note that the parentheses around the input type are only required as of Swift 3+.