> On May 13, 2016, at 7:30 AM, Dave Abrahams <dabrah...@apple.com> wrote: > > > on Mon May 09 2016, Joe Groff <jgroff-AT-apple.com> wrote: > >>> On May 9, 2016, at 6:23 PM, Brent Royal-Gordon via swift-evolution >>> <swift-evolution@swift.org> wrote: >>> >>>> * Operations that depend on sorted-ness and use binary predicates should >>>> not be available on all Collections; they're too easy to misuse, >>>> they're hard to name well, and as Nicola Salmoria has noted, they >> >>>> would not make any sense at all for a Set<T>. >>>> >>>> * They should be scoped to a kind of collection that bundles >>>> the predicate with the elements, e.g. >>>> >>>> let x = Sorted([3, 4, 1, 5, 2], >) // stores a sorted copy of >>>> the array >>>> let y = Sorted(preSorted: 0..<100, <) // stores a copy of the range >>>> >>>> Maybe there should also be protocols for this; CountableRange<T> would >>>> already already conform to the immutable version. We might want a >>>> mutable form of the protocol for sorted collections with >>>> insertion/removal methods. This whole area needs more design. >>> >>> I agree with both of these statements, but not with your conclusion. >>> >>> There are three classes of collections: >>> >>> 1) Those which are always sorted, like a SortedSet. >>> 2) Those which may or may not be sorted, like an Array. >>> 3) Those which are never sorted, like a Set. >>> >>> These APIs are useless on a #3, but #2 is still a valuable use case >>> to support. In particular, it's quite common to use sorted `Array`s, >>> and these APIs would help you do that. >>> >>> What I might consider doing is tying this to >>> `RangeReplaceableCollection`. That protocol is applied only to types >>> which allow insertion at arbitrary indices, which is a good, though >>> not perfect, proxy for types which might allow you to manually >>> maintain a sort order. `Array`, `ArraySlice`, `ContiguousArray`, and >>> the mutable `String` views would get these methods, while `Set` and >>> `Dictionary` would not. >> >> We could also introduce a new OrderedCollection protocol. (This would >> also be useful in the future for supporting `case` pattern matching on >> collections. It makes sense to pattern-match arrays and other ordered >> collections in order by element, but you'd expect very different >> semantics pattern-matching an unordered Set.) > > What do you mean by “Ordered” here? Please note that when Cocoa uses > “Ordered” it means something very different from “Sorted.” I don't find > the Cocoa usage intuitive myself, but it might be best to avoid that > term to avoid confusion.
By "ordered", I only mean "ordering is significant to the value of the collection", so Array is ordered but Set is not. -Joe _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution