[Stdlib] For Collections, the SubSequence of a Subsequence is SubSequence #8888
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There's a more pervasive issue here that needs further study; essentially, we can end up with self-derived sources getting reinjected later, and will either need to avoid that reinjection or need to expand what this localized hack does, filtering out self-derived constraints when we enumerate requirements.
…ence. Part of ABI FIXME apple#99, this gives us some nice consistency that ensures that slicing a SubSequence gives us another SubSequence. There are two source-compatibility implications to this change: * Collections now need to satisfy this property, which could not be expressed in Swift 3. There might be some Collections that don't satisfy this property, and will break with the Swift 4 compiler *even in Swift 3 compatibility mode*. Case in point... * The Lazy collection types were formulated as a lazy collection of the base slice (e.g., LazyCollection<ArraySlice<T>>) rather than as a slice of the lazy collection (e.g., Slice<LazyCollection<Array<T>>). The former doesn't meet the new requirements, so change to the latter.
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@swift-ci please smoke test |
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@dabrahams and @airspeedswift , you'll be interested in this because it affects compatibility |
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@airspeedswift specifically, it changes the |
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Part of ABI FIXME #99, this gives us some nice consistency that
ensures that slicing a
SubSequencegives us anotherSubSequence. Thereare two source-compatibility implications to this change:
expressed in Swift 3. There might be some Collections that don't
satisfy this property, and will break with the Swift 4 compiler
even in Swift 3 compatibility mode. Case in point...
the base slice (e.g.,
LazyCollection<ArraySlice<T>>) rather than asa slice of the lazy collection (e.g.,
Slice<LazyCollection<Array<T>>). The former doesn't meet the newrequirements, so change to the latter.