[swift-users] Multiple value-binding patterns in a single switch case

[Glen Huang]

Yes, not all animals have names.

Defining a protocol sounds reasonable.

In my case, the Animal, Dog and Cat are all subclasses of Core Data's NSManagedObject, having to define a protocol and make them conform to that is a bit involved. 

But I think that seems to be the only sensible way.

Thanks.

> On 9 Jun 2017, at 7:28 PM, Jens Persson <jens at bitcycle.com> wrote:
> 
> I'm not sure what you are trying to achieve.
> Why can't you just do:
> label.text = animal.nam
> ?
> Is it because not all Animals have names?
> If so, you could perhaps use something like this:
> 
> class Animal {}
> protocol Named {
>     var name: String { get }
> }
> class Dog: Animal, Named {
>     let name = "Dog"
> }
> class Cat: Animal, Named {
>     var name: String {
>         return "Cat"
>     }
> }
> 
> let animals: [Animal] = [Cat(), Dog()]
> 
> for animal in animals {
>     if let namedAnimal = animal as? Named {
>         print(namedAnimal.name)
>     }
> }
> 
> 
> 
> 
> On Fri, Jun 9, 2017 at 12:34 PM, Glen Huang via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
> Hi, I wonder what's the correct way to express something like this in swift:
> 
> Say I have a superclass with two subclasses:
> 
> class Animal {}
> class Dog: Animal {
>     let name = "Dog"
> }
> class Cat: Animal {
>     var name: String {
>         return "Cat"
>     }
> }
> 
> And I want to display the name with a switch:
> 
> switch animal {
> case let a as Dog, let a as Cat:
>     label.text = a.name <http://a.name/>
> default:
>     break
> }
> 
> Swift currently won't allow me to use multiple value-binding patterns like this. I wonder what's the right way to express it? Must I repeat the statements?
> 
> switch animal {
> case let a as Dog:
>     label.text = a.name <http://a.name/>
> case let a as Cat:
>     label.text = a.name <http://a.name/>
> default:
>     break
> }
> 
> I also tried fallthrough, but swift won't let me fall through to a value-binding pattern:
> 
> switch animal {
> case let a as Dog:
>     fallthrough // error
> case let a as Cat:
>     label.text = a.name <http://a.name/>
> default:
>     break
> }
> 
> I'm at my wits end. Could someone shed some light on this? Thanks.
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