> On May 9, 2016, at 6:23 PM, Brent Royal-Gordon via swift-evolution > <[email protected]> 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.) -Joe _______________________________________________ swift-evolution mailing list [email protected] https://lists.swift.org/mailman/listinfo/swift-evolution
