Re: Why does switch require a full declaration?

why do you deéclaire:

let _ : UISwipeGestureRecognizerDirection = .up

It seems it is nowhere used.

for the switch, you should try :

let dir : UISwipeGestureRecognizerDirection = sender.direction

switch dir {
case .up: 

}

PRobably the compiler has has problem with type inference.

UISwipeGestureRecognizerDirection is not an enum, it’s an option set.  Consider this:

let _: UISwipeGestureRecognizerDirection = [.up, .down]
let _: UISwipeGestureRecognizerDirection = [.up]
let _: UISwipeGestureRecognizerDirection = .up

The first line demonstrates that the option set can contain many values.  The second line shows the ‘standard’ way of writing a single value option.  The last line, the one you had, is a convenient way to write the second line.

All of the above work because the type declaration establishes a scope in which the compiler can look for values.  This doesn’t work in a switch statement because a switch statement only creates that scope when you give it an enum (in the Swift grammar this is the difference between the expression-pattern and the enum-case-pattern).

The above just covers why UISwipeGestureRecognizerDirection behaves differently than a standard enum; it doesn’t really address the issue of whether this is just a current limitation or something more fundamental.  I don’t know enough about the internals to comment on that.  I recommend you file an enhancement for this to be improved and we’ll see where that gets you.

Please post your bug number, just for the record.

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