This wasn’t the default behaviour because `enumerated()` is a method for the `Sequence` protocol, which doesn’t have any indices. Integers are the only thing that make sense there. But I agree that this should have been part of the standard library already.
> +1.One of those things where you wonder why this wasn't the default behavior. > > ~Robert Widmann > > 2016/09/28 14:23、Nevin Brackett-Rozinsky via > swift-evolution<swift-evolution@swift.org(mailto:swift-evolution@swift.org)>のメッセージ: > > > +1, I have been mildly surprised that this was not already present. > > > > My workaround heretofore has been: > > > > for idx in abc.indices { > > let val = abc[i] > > // do something with idx and val > > } > > > > Nevin > > > > > > On Wed, Sep 28, 2016 at 1:55 PM, Erica Sadun via > > swift-evolution<swift-evolution@swift.org(mailto:swift-evolution@swift.org)>wrote: > > > Gist here:https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2 > > > > > > Introducingindexed()collections > > > Proposal: TBD > > > Author:Erica Sadun(https://github.com/erica),Nate > > > Cook(https://github.com/natecook1000),Jacob > > > Bandes-Storch(https://github.com/jtbandes),Kevin > > > Ballard(https://github.com/kballard) > > > Status: TBD > > > Review manager: TBD > > > > > > Introduction > > > > > > This proposal introducesindexed()to the standard library, a method on > > > collections that returns an (index, element) tuple sequence. > > > > > > > > > Swift-evolution thread:TBD(https://gist.github.com/erica/tbd) > > > > > > Motivation > > > > > > The standard library'senumerated()method returns a sequence of pairs > > > enumerating a sequence. The pair's first member is a monotonically > > > incrementing integer starting at zero, and the second member is the > > > corresponding element of the sequence. When working with arrays, the > > > integer is coincidentally the same type and value as anArrayindex but the > > > enumerated value is not generated with index-specific semantics. This may > > > lead to confusion when developers attempt to subscript a non-array > > > collection with enumerated integers. It can introduce serious bugs when > > > developers useenumerated()-based integer subscripting with non-zero-based > > > array slices. > > > > > > > > > Indices have a specific, fixed meaning in Swift, which are used to create > > > valid collection subscripts. This proposal introducesindexed()to produce > > > a more semantically relevant sequence by pairing a > > > collection'sindiceswith its members. While it is trivial to create a > > > solution in Swift, the most common developer approach shown here > > > calculates indexes twice: > > > > > > extension Collection { /// Returns a sequence of pairs (*idx*, *x*), > > > where *idx* represents a /// consecutive collection index, and *x* > > > represents an element of /// the sequence. func indexed() > > > ->Zip2Sequence<Self.Indices, Self>{ return zip(indices, self) } } > > > > > > Incrementing an index in some collections can be unnecessarily costly. In > > > a lazy filtered collection, an index increment is potentially O(N). We > > > feel this is better addressed introducing a new function into the > > > Standard Library to provide a more efficient design that avoids the > > > attractive nuisance of the "obvious" solution. > > > > > > Detailed Design > > > > > > Our vision ofindexed()bypasses duplicated index generation with their > > > potentially high computation costs. We'd create an iterator that > > > calculates each index once and then applies that index to subscript the > > > collection. Implementation would take place throughIndexedSequence, > > > similar toEnumeratedSequence. > > > > > > Impact on Existing Code > > > > > > This proposal is purely additive and has no impact on existing code. > > > > > > Alternatives Considered > > > Not yet > > > > > > > > > > > > _______________________________________________ > > > swift-evolution mailing list > > > swift-evolution@swift.org(mailto:swift-evolution@swift.org) > > > https://lists.swift.org/mailman/listinfo/swift-evolution > > > > > > > _______________________________________________ > > swift-evolution mailing list > > swift-evolution@swift.org(mailto:swift-evolution@swift.org) > > https://lists.swift.org/mailman/listinfo/swift-evolution > > > _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
