Variable outside DispatchQueue.main.async is empty - swift

Question

I tried to resolve this error since days but I dont understand why am I getting this error in the first place.
Please help...
func createData(request:Crudpb_CreateRequest) -> String {
DispatchQueue.main.async {
self.response = try! self.client.create(request)
print("This is response 1: " + self.response.result) // <-------- This is priting the right response
}
print("This is response outside DispatchQueue: " + self.response.result) // <------- This is not printing anyvalue
return self.response.result // <------ This is not
}

Answer 1

You are dispatching whatever work you are doing in your create request method asynchronously, therefor your create data function will not wait for this work to be done to continue its execution, it just calls it and keeps its execution and thats why your value is not modified when you reach your "This is response outside DispatchQueue: " statement.
It will be modified in the capture block that you have created, thats why you need to create an #escaping completion block like they mentioned before, to only return your value when the work you did to obtain it is finished.
func createData(request:Crudpb_CreateRequest, with completion: #escaping (String) -> Void) {
DispatchQueue.main.async {
self.response = try! self.client.create(request)
completion(self.response)
}
}

Answer 2

This is the way I use #escaping closures: You don't need a return value in the function, given that the execution of the calling function may end before the closure is finished. You also need to specify a dataType in the #escaping parameter (Bool in this case)... also, Function types cannot have argument labels, so you must use "_"
self.fetchStuff(onCompletion: { (success) in
if success {
// Do something
}
})
func fetchStuff(onCompletion: #escaping (_ success: Bool) -> Void) {
// Do some asynch stuff
onCompletion(true)
}