> On Sep 15, 2017, at 12:40 PM, Joanna Carter via swift-users
> <swift-users@swift.org> wrote:
>
> Xcode Version 9.0 (9A235)
>
> Hmmm. I'm now getting a segmentation fault : 11 on a constructor when trying
> to implement type erasure :
Swift 4.0 had issues with members and member references named ‘subscript’. On
master, I get the correct error message without crashing:
Slavas-MBP:swift slava$
../build/Ninja-ReleaseAssert/swift-macosx-x86_64/bin/swiftc sub.swift
sub.swift:22:17: error: value of type 'providerType' has no member 'subscript'
_subscript = base.subscript
^~~~ ~~~~~~~~~
Indeed you’re not supposed to be able to refer to a subscript member like this.
You could use a keypath, or try some other approach.
Slava
>
> protocol DataProvider
> {
> associatedtype ItemType
>
> subscript(index: Int) -> ItemType { get }
> }
>
> class _AnyDataProviderBoxBase<itemType>: DataProvider
> {
> subscript(index: Int) -> itemType
> {
> fatalError()
> }
> }
>
> class _AnyDataProviderBox<providerType: DataProvider>:
> _AnyDataProviderBoxBase<providerType.ItemType>
> {
> private let _subscript: (_ index: Int) -> providerType.ItemType
>
> init(_ base: providerType) // segmentation fault : 11
> {
> _subscript = base.subscript
> }
>
> override subscript(index: Int) -> providerType.ItemType
> {
> return _subscript(index)
> }
> }
>
> final class AnyDataProvider<providerType : DataProvider>: DataProvider
> {
> private let box: _AnyDataProviderBox<providerType>
>
> init(_ base: providerType)
> {
> self.box = _AnyDataProviderBox(base)
> }
>
> subscript(index: Int) -> providerType.ItemType
> {
> return box[index]
> }
> }
>
> Joanna
>
> --
> Joanna Carter
> Carter Consulting
>
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