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iOS Build a Weather App with Swift Managing Complexity Callback Methods With Closures

Why the following code is not accepted as valid?

I Code Challage "callback-methods-with-closures" I am posting the following answer:

typealias BlogPostCompletion = (data: NSData!, response: NSURLResponse!, error: NSError!) -> Void

func fetchTreehouseBlogPosts (completion : BlogPostCompletion) { }

It is asking me to make sure that the method name is fetchTreehouseBlogPosts and to check that the syntax is right. I don't understand where the code is wrong! I have checked it in a playground and works fine without any syntax error

Callbacks.swift
import Foundation

// Add your code below

typealias BlogPostCompletion = (data: NSData!, response: NSURLResponse!, error: NSError!) -> Void

func fetchTreehouseBlogPosts (completion : BlogPostCompletion) {
}

2 Answers

Richard Lu
Richard Lu
20,185 Points

I remember this challenge and I changed the return type for the signature to '()' instead of void. This worked for me. You are absolutely correct, but I think it's just a preference that treehouse has.

typealias BlogPostCompletion = (NSData!, NSURLResponse!, NSError!) -> ()

No, it still isn't working! pretty strange!!

Roberta Voulon
Roberta Voulon
5,792 Points

I think a ton of people are stuck on this, I finally got a hint from somewhere and it worked for me, so I'm re-posting this where I can: What made it work for me in the end was wrap the signature in outer parenthesis like this:

typealias BlogPostCompletion = ((NSData!, NSURLResponse!, NSError!) -> Void)
func fetchTreehouseBlogPosts(completion: BlogPostCompletion) {}

You shouldn't have to do this though! It's perfectly valid without the wrapping parentheses.

Yes, that did the trick for me as well! Got the hint from another post. :)