> On Apr 14, 2016, at 2:03 PM, Milos Rankovic <mi...@milos-and-slavica.net>
> wrote:
>> On 14 Apr 2016, at 21:36, John McCall <rjmcc...@apple.com
>> <mailto:rjmcc...@apple.com>> wrote:
>>
>> No, you just need Tree to conform to both ArrayLiteralConvertible and
>> IntegerLiteralConvertible, and it implements the latter by building a Value
>> out of it.
>
> You mean this:
>
> public enum IntTree {
> case Leaf(Int)
> case Branches([IntTree])
> }
>
> extension IntTree : ArrayLiteralConvertible {
> public init(arrayLiteral elements: IntTree...) {
> self = .Branches(elements)
> }
> }
>
> extension IntTree : IntegerLiteralConvertible {
> public init(integerLiteral value: IntegerLiteralType) {
> self = .Leaf(value)
> }
> }
>
> let tree: IntTree = [[], 1, [2, 3], [[4, 5], [6, 7], [8, 9]]]
>
>> you'll simply have to make your Tree less generic
>
>
> Yep, that’s the rub… With generic trees you can express yourself freely,
> whether you feel like:
>
> import SpriteKit
>
> let actionTree: Tree<SKAction> = [
> ◊.waitForDuration(1),
> [
> ◊.fadeInWithDuration(1),
> ◊.scaleTo(1, duration: 1)
> ],
> ◊.playSoundFileNamed("TaDa", waitForCompletion: false)
> ]
>
> … or:
>
> let johnny: DictionaryTree<String, JSONValue> =
> [
> "name": ◊"Johnny Appleseed",
> "age": ◊25,
> "address": [
> "house_number": ◊21,
> "street": ◊"2nd Street",
> "city": ◊"New York"
> ]
> ]
>
> I’d just love to get rid of that prefix operator…
Note that all of your examples rely not just on recursion but on heterogeneous
recursion, so the multiple-conformance idea doesn't work. Fundamentally, your
trees have a payload type that needs to be constructible from different kinds
of literal. It's appropriate to model that with conformance to multiple
protocols. The ability to do that conditionally based on whether another type
declares a conformance is called "conditional conformance", and it's already
something we're strongly considering for the future; it's just not an easy
feature to actually implement.
John.
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