Why sometime we use -> void for completion handler in swift but sometime not? -

i have watched 2 tutorial. first 1 basic completion handler in swift. tutor shows example of code:

func istextvalid(input: string, completion: (result: bool) -> void) {      if (input == "hello") {         completion(result: true)     }else{         completion(result:false)     } }   istextvalid("hello", { (result) -> void in     if (result == true) {         println("people hello")     }else{         println("people not hello")     } }) 

the second tutorial http request code looks this:

        /* 4. make request */     let task = session.datataskwithrequest(request) {data, response, downloaderror in          if let error = downloaderror {             println("could not complete request \(error)")         } else {              /* 5. parse data */                             var parsingerror: nserror? = nil             let parsedresult = nsjsonserialization.jsonobjectwithdata(data, options: nsjsonreadingoptions.allowfragments, error: &parsingerror) as! nsdictionary              /* 6. use data! */                             if let error = parsingerror {                 println(error)             } else {                 if let results = parsedresult["results"] as? [[string : anyobject]] {                     self.movies = movie.moviesfromresults(results)                     dispatch_async(dispatch_get_main_queue()) {                         self.tableview.reloaddata()                     }                 } else {                     println("could not find results in \(parsedresult)")                 }             }         }     }      /* 7. start request */     task.resume() 

you can see first line of code doesn't have return void in first tutorial, why?

what return void anyway? why have type return void?

the use of void optional same way can declare function or without void can declare completion handler or wihtout

func noreturn() -> void 

is identical

func noreturn() 

for completion handles when declaring it:

func istextvalid(input: string, completion: (result: bool) -> void)  

is equals

func istextvalid(input: string, completion: (result: bool) -> ())  

for completion handles when calling it:

(result) -> void in 

is equals

(result) in