@Venom
just got a chance to look at it.
I opened up my old example and it’s actually still working.
I thought they changed it with Swift 1.2 , but I was thinking of something slightly different.
Mine is compiling without a problem.
The only difference is that I first declare my variable as a Double and then use it.
So I do:
var amount: Double!
or you can do
var amount = Double(50)
and then you can do:
amount = (amountTextField.text as NSString).doubleValue
However I tried it your way too, where you declare and use it at the same time and I
was able to do it without the compiler complaining about anything…
So I looked at your code again and now I see that I’ve totally missed what the problem is 
Problem is that your text field is an optional value - basically you are not guaranteeing that it has any value. So the compiler it’s just telling you that it cannot convert it if there is no value.
So either do a ‘if let’ first, or just make sure you have a value in it and force unwrap the .text using ‘!’
I would say it’s probably best to check. ( my last comment )
Just do:
if let amountAsNsString = amountTextField.text as! NSString {
var amount = amountAsNsString.doubleValue
…