[swift-users] Strange type error

[zhigang]

It might have something to do with

`setSubscriptee`

with seems from the implementation is a `mutating` operation.

If you comment it out, or just give it a empty callback, it will pass
compile.


Kyle

On Tue, Mar 22, 2016 at 6:23 AM Howard Lovatt via swift-users <
swift-users at swift.org> wrote:

> Hi,
>
> I don't understand your comment, can you explain some more please?
>
> Thanks,
>
>  -- Howard.
>
>
> On Monday, 21 March 2016, zh ao <owenzx at gmail.com> wrote:
>
>> You protocol is not defined properly.
>>
>> On Mon, Mar 21, 2016 at 7:08 AM, Howard Lovatt via swift-users <
>> swift-users at swift.org> wrote:
>>
>>> HI,
>>>
>>> Does anyone know what is happening here:
>>>
>>> protocol Subscriptable {
>>>
>>>     associatedtype Element
>>>
>>>     associatedtype Index
>>>
>>>     var firstIndex: Index { get }
>>>
>>>     var lastIndex: Index { get }
>>>
>>>     subscript(index: Index) -> Element { get set }
>>>
>>> }
>>>
>>>
>>> struct AllSubscriptable<E, I>: Subscriptable {
>>>
>>>     typealias Element = E
>>>
>>>     typealias Index = I
>>>
>>>     let firstIndexee: () -> I
>>>
>>>     let lastIndexee: () -> I
>>>
>>>     let subscriptee: (index: I) -> E
>>>
>>>     let setSubscriptee: (index: I, element: E) -> Void
>>>
>>>     var firstIndex: I { return firstIndexee() }
>>>
>>>     var lastIndex: I { return lastIndexee() }
>>>
>>>     subscript(index: I) -> E {
>>>
>>>         get { return subscriptee(index: index) }
>>>
>>>         set { setSubscriptee(index: index, element: newValue) }
>>>
>>>     }
>>>
>>> }
>>>
>>>
>>> extension Array {
>>>
>>>     var asScriptable: AllSubscriptable<Element, Int> {
>>>
>>>         return AllSubscriptable(
>>>
>>>             firstIndexee: { return self.startIndex }, // Error: Cannot
>>> convert `() -> Int` to expected `() -> _`
>>>
>>>             lastIndexee: { return self.endIndex },
>>>
>>>             subscriptee: { return self[$0] },
>>>
>>>             setSubscriptee: { self[$0] = $1 }
>>>
>>>         )
>>>
>>>     }
>>>
>>> }
>>>
>>>
>>> The error, "Cannot convert `() -> Int` to expected `() -> _`", on the
>>> `firstIndexee` closure is very strange since the types are correct and the
>>> same as `lastIndexee` which does not have an error.
>>>
>>> Also if the set subscript in Subscriptable and then all the other set
>>> support in AnySubscriptabe and in the extension is removed, then no error.
>>>
>>> Any clues to why?
>>>
>>> -- Howard.
>>>
>>> _______________________________________________
>>> swift-users mailing list
>>> swift-users at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-users
>>>
>>>
>>
>
> --
> -- Howard.
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
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