'bool' is not convertible to 'uint8' - swift

Question

I'm trying to build to-do app using Xcode 6 and Swift. I was able to run the app on Xcode 6 dp2 but after updating to dp7 I'm getting this error:
'bool' is not convertible to 'uint8'.
Here is the function with the error:
override func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject?) {
**if ((segue && segue!.identifier == "showdetails") != nil)**{
var selectedIndexPath:NSIndexPath = self.tableView.indexPathForSelectedRow()
var detailViewController:DetailViewController = segue!.destinationViewController as DetailViewController
detailViewController.toDoData = toDoItems.objectAtIndex(selectedIndexPath.row) as NSDictionary
}
}

Answer 1

The correct way to write that is:
if (segue != nil && segue!.identifier == "showdetails") {
but an even better way is using optional binding:
if let segue = segue {
if (segue.identifier == "showdetails") {
Note that there are other errors about incorrect usage of optionals. This is the modified code that compiles in playground:
if let segue = segue {
if (segue.identifier == "showdetails") {
var selectedIndexPath:NSIndexPath? = self.tableView.indexPathForSelectedRow()
if let selectedIndexPath = selectedIndexPath {
var detailViewController:DetailViewController = segue.destinationViewController as DetailViewController
detailViewController.toDoData = toDoItems.objectAtIndex(selectedIndexPath.row) as NSDictionary
}
}
}
indexPathForSelectedRow returns an optional, so you have to account for that.
Update: as pointed out by #MartinR, segue is no longer optional, so you can solve the problem by simply updating the function signature, and its implementation should look like:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if (segue.identifier == "showdetails") {
var selectedIndexPath = self.tableView.indexPathForSelectedRow()
if let selectedIndexPath = selectedIndexPath {
var detailViewController = segue.destinationViewController as DetailViewController
detailViewController.toDoData = toDoItems.objectAtIndex(selectedIndexPath.row) as NSDictionary
}
}
}

Answer 2

First of all when I read the documentation what I read is :
func prepareForSegue(_ segue: UIStoryboardSegue, sender sender: AnyObject?)
UIKit seems to be updated in Beta7 to use less optionals. So segue may be not optional.
Then even if your function signature is good, you are comparing a Boolean to nil.
This (segue && segue!.identifier == "showdetails") is a boolean. A boolean is either true or false.
And at the very end, here is the best practice to unwrap a variable :
if let mySafeVariable = myOptionalVariable {
if mySafeVariable.attribute == <Whatever> {
}
}
You should. No, wait, you must read the Swift free iBooks.