> On Apr 5, 2017, at 9:43 PM, Brent Royal-Gordon via swift-evolution > <swift-evolution@swift.org> wrote: > >> On Apr 5, 2017, at 5:45 PM, Ben Cohen via swift-evolution >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >> >> • What is your evaluation of the proposal? > > (As a meta issue, I'm not sure I like the grab-bag review style; I'm finding > this proposal a little bit difficult to navigate.) > > Sequence-based initializer and merging initializer > > Good idea, but I think these two are redundant with each other, and I don't > think "merging" is an accurate way to describe what the second one does. > (`merging` would suggest to me that it was combining several dictionaries or > lists, not combining conflicting elements.) I'd suggest a single initializer > along the lines of: > > init<S: Sequence>(_ keysAndValues: S, correctingConflictsBy > resolveConflict: (Value, Value) throws -> Value = { fatalError("Duplicate > values \($0) and \($1)") }) rethrows > where S.Iterator.Element == (key: Key, value: Value)
Thanks for all your feedback, Brent! One note on this item in particular—if you specify a default argument for a throws/rethrows closure, you have to use "try" at the call site even if the default closure argument doesn't throw. Modules currently don't promise that default closure arguments don't throw, and a default argument could change from non-throwing to throwing in a later version of a library. There's a bug tracking the issue here: https://bugs.swift.org/browse/SR-2979 > Merging methods > > Good idea, but I'm not a fan of the `mergingValues:` label. I would suggest > the same `correctingConflictsBy resolveConflict:` label I suggested for the > previous method—possibly including the default value. I also think > `merge(_:correctingConflictsBy:)`'s first parameter should be labeled `with`, > just as the `merged` variant is. > > I wonder if we might also want a method that copies the Dictionary, but with > a single key added/removed/changed: > > func withValue(_ value: Value?, forKey key: Key) -> [Key: Value] > > Key-based subscript with default value > > I like the functionality, but not way this proposal does it. I don't like > having the default value be a labeled parameter to the subscript, because it > isn't used to locate the value. However, I can't come up with a better syntax > without adding language features. What I'd like to do is make it possible to > assign through `??`: > > frequencies[c] ?? 0 += 1 > > But that would require either that we support `inout` functions, or that `??` > become magic syntax instead of a standard library feature. The former is not > coming in Swift 4 and the latter is less than ideal. > > Still, if we would rather have that syntax and we think we'll soon have the > language improvements needed to pull it off, I'd suggest rejecting this > portion of the proposal. > > Dictionary-specific map and filter > > I am +114 on this. I say that because I have received 114 upvotes on my Stack > Overflow answer explaining how to write a `Dictionary.map` method: > <http://stackoverflow.com/questions/24116271/whats-the-cleanest-way-of-applying-map-to-a-dictionary-in-swift/24219069#24219069 > > <http://stackoverflow.com/questions/24116271/whats-the-cleanest-way-of-applying-map-to-a-dictionary-in-swift/24219069#24219069>> > > I agree with the decision not to pass keys to the closures in these methods; > that keeps them simple and focused, and ensures they stay parallel with > ordinary `map` and `filter`. I also agree with the decision to not build in a > form of `map` which allows key remapping; you can always do that with the > sequence-based initializer, which would let you add conflict-handling logic > more elegantly than a key-value `map` could. > > Visible dictionary capacity > > I doubt I'll ever use the `capacity` property, but I'm not opposed to it. > Adding a `reserveCapacity(_:)` method is a good idea. > > A grouped(by:) method for sequences > > Yes, please. > > Apply relevant changes to Set > > These make sense. (I considered suggesting the `filter` method be called > `intersection(where:)`, but on second thought, I don't think that conveys the > actual use cases for the method very well.) > > I wonder if we might want to conform `Dictionary` to `SetAlgebra`. They have > compatible semantics, and I've occasionally wanted to use them in the same > places. On the other hand, some of the methods might form attractive > nuisances; perhaps I should just write a SetAlgebra-conforming view when I > want to do that. > > General notes > > If SE-0161 is accepted, we may want to support key path variants of some of > these APIs (like `grouped(by:)`, `map(_:)`, and `filter(_:)`). On the other > hand, we may want to defer that so we can consider that issue holistically, > including with existing Collection APIs. > >> • Is the problem being addressed significant enough to warrant a change >> to Swift? > > Yes. These are all common needs; when working with dictionaries, I find > myself writing `for` loops with `var`s far more often than I'd like. > >> • Does this proposal fit well with the feel and direction of Swift? > > Yes, these are all pretty straightforward additions. > >> • If you have used other languages or libraries with a similar feature, >> how do you feel that this proposal compares to those? > > Ruby's `Hash` has many of these features and I appreciate them there; > `NSDictionary` does not and it suffers for it. Perl hashes have a flattening > behavior that tends to be amenable to editing them in various ways, but > that's not really suitable for Swift. > >> • How much effort did you put into your review? A glance, a quick >> reading, or an in-depth study? > > > Quick reading. > > -- > Brent Royal-Gordon > Architechies > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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