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The Joys of Beta Swift: as Versus as! and Why I Avoid Betas
It came to my attention this week there’s a big change to Swift code on the way. It doesn’t look big though: it is the difference between as and as!.
The keyword as is the conversion operator. Usually type or class are easily defined like this:
var myColor = UIColor() //class UIColor var myNumber:Integer = 0 //type Integer
But there are times you get things like this in table views and collection views:
let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath)
The method of dequeueReusableCellWithIdentifier returns AnyObject, which is so generic it is worthless. We need to downcast it to UITableViewCell to use it.
let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as UITableViewCell
If the class does not exist or the class is incompatible with the cast, you get an error. For documentation purposes, Apple changed as to as! for these cases so anyone reading your code knows an error could occur. In Swift 1.2 Beta this should be
let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as! UITableViewCell
This does not work before 1.2 though. Don’t try it unless you have a Xcode 6.3 beta.
Speaking of betas, I want to be clear about my policy about betas:
Unless there is no production version, I always write to the production version. I suggest unless you seriously know what you are doing and don’t care to actually get something in the App Store quickly to avoid beta versions. There are four reasons for this:
- Apple does not accept code from beta versions. For most cases where there is a production version or GM seed, you write an app in Beta you have to wait till they release it as a production version before they even accept your code. If Apple holds up release of XCode due to hardware issues with the Apple Watch for example your iPhone app will be stuck for months without a production release and months of lost sales.
- Betas change often. What you write and what will be the production version is different. That might mean several versions of coding — and a lot of wasted effort and time.
- Betas are poorly documented. Trying to understand release notes which often are the only place that explains a change is not easy.
- You don’t talk about betas. Apple has been very loose about their usual non-disclosure on Swift betas( I’m hoping that the case above), but that said, if they change their mind at any time, they can yank your license for disclosing features of a beta version. Many betas come with a Non-disclosure agreement. Break it and you could be punished.
So I make it a policy not to use betas unless I have to. I did between June 2014 and October 2014 because there was nothing else for Swift. And I had to change this entire website several times because of that. I could delay my book launch for months due to this change, or use the production version and get it out in March. Those working on Apple watch projects as of this writing have to use a beta. They have no choice. If you have a choice of beta and a production version, Pick the production.
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