[swift-users] Using 'SomeProtocol' as a concrete type conforming to protocol 'SomeProtocol' is not supported

[Nevin Brackett-Rozinsky]

It will work if you change the enum declaration to:

enum ElementNode<T>

In other words, let the enum hold arbitrary unconstrained associated types,
and then make your APIs utilize instances of the enum with the associated
type constrained to a protocol.

The specific example you provide is essentially equivalent to:

var childElements = [Element?]()

Nevin


On Wed, Dec 28, 2016 at 6:41 PM, Brandon Knope via swift-users <
swift-users at swift.org> wrote:

> I don’t understand why this is a problem
>
> protocol Element {
>
>
> }
>
> enum ElementNode<T: Element> {
>     case element(T)
>     case empty
> }
>
> var childElements = [ElementNode<Element>]()
>
> I need to represent an array of my nodes that could be multiple kinds of
> elements
>
> Is there a workaround?
>
> Brandon
>
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