[swift-evolution] Why doesn't Collection's SubSequence conform to Collection?
davide at gokarumi.com
Fri Feb 24 09:49:55 CST 2017
What's the status of Recursive protocol constraints? it's a feature that
will help the design of a library I'm working on.
How can I help ?
On Tue, Feb 14, 2017 at 1:32 AM Douglas Gregor via swift-evolution <
swift-evolution at swift.org> wrote:
> On Feb 13, 2017, at 1:42 PM, Charles Srstka via swift-evolution <
> swift-evolution at swift.org> wrote:
> The following comment accompanies the declaration of the SubSequence
> associated type in the Collection protocol:
> /// A sequence that represents a contiguous subrange of the collection's
> /// elements.
> /// This associated type appears as a requirement in the `Sequence`
> /// protocol, but it is restated here with stricter constraints. In a
> /// collection, the subsequence should also conform to `Collection`.
> associatedtype SubSequence : IndexableBase, Sequence = Slice<Self>
> The comments clearly state that the subsequence should conform to
> Collection, however, it is not declared as such. Why is this?
> The compiler doesn’t support “recursive” constraints. We’re working on it
> - Doug
> swift-evolution mailing list
> swift-evolution at swift.org
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