<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Some belated feedback.</div><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 16, 2017, at 6:39 PM, Ben Cohen via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class="">Here is a list of commonly requested algorithms to operate on <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Sequence</code> or <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Collection</code>:</p><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class="">In-place transformations:<ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 0px;" class=""><li style="box-sizing: border-box;" class="">transform elements in a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">MutableCollection</code> using a closure i.e. in-place <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">map</code></li></ul></li></ul></div></div></blockquote><div>+0.5 in the stdlib if only to side-step numerous re-implementations and perhaps also for minor performance gains.</div><div><br class=""></div><div>+0.5 if it’s paired with an in-place variant (`mutating func mapInPlace(_ transform: (inout Element) -> Void) -> Void`); could perhaps be better-named `updateEach`.</div><div><br class=""></div><div>Both are minor but would be nice-to-have as built-ins.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 0px;" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">remove(where:)</code> that takes a predicate i.e. in-place <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">filter</code></li></ul></li></ul></div></div></blockquote><div>+2 as long as this is an overridable method. It’s a common need and difficult for users to write an efficient implementation.</div><div><br class=""></div><div>One quibble: would this be on `Collection`, `MutableCollection`, or some new `ShrinkableCollection`? This issue I’d have with putting this onto `Collection` itself is that that would seemingly shut the door on `Collection` being adoptable by any type that implements a “collection” with some fixed, intrinsic size.</div><div><br class=""></div><div>Thus either adding it to `MutableCollection` (at cost of being overly narrow) or adding it to some new refinement like `ShrinkableCollection` (thus allowing e.g. `Set` and `Dictionary` to conform w/out eliminating fixed-size “collections” from adopting `Collection`).</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 0px;" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">remove(indices:)</code> that takes a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Sequence</code> of <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Index</code></li></ul></li></ul></div></div></blockquote><div>+0 if *exactly* as stated; the point of a method like this would presumably be efficient bulk-removal, and a mere “a `Sequence` of `Index`” doesn’t provide much useful information: no count, no guarantee each index is included at-most once, no guarantee of ordering, and so on.</div><div><br class=""></div><div>I think the “right” eventual solution is an equivalent to `(NS)IndexSet`—loosely speaking, a “collection” of non-empty, non-overlapping, ordered-ascending ranges of indices—but unfortunately it seems both difficult and premature to contemplate such a thing at this time.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 0px;" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class="">bulk operations (<code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">replace</code>, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">remove</code>, <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">insert</code>) on <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">RangeReplaceableCollection</code> for a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Sequence</code> of subranges</li></ul></li></ul></div></div></blockquote><div>See above: a `Sequence` of subranges is a bit better than a `Sequence` of `Index`, but doesn’t provide much information (# of ranges? # of indices? ranges ordered somehow? ranges non-overlapping? ranges non-empty?).</div><div><br class=""></div><div>Thus for both of the previous two I strongly think building them around an `(NS)IndexSet`-like component is the way to do them but to do that `(NS)IndexSet`-alike type properly would IMHO be a bigger project than the current scope; in the absence of such an index-set type I’m not sure there’s enough benefit to these bulk operations to justify their inclusion.</div><div><br class=""></div><blockquote type="cite" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Select a random element of a <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">RandomAccessCollection</code> (note this could include a random element of <code class="" style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">0..<n</code>)</li></ul></div></blockquote><div>+1 to add to the stdlib some reasonable way to draw a value at random from `0..<n` along with the obvious convenience method on `RandomAccessCollection`. Especially with cross-platform ambitions having the stdlib provide a non-terrible way to do this seems prudent.</div><div><br class=""></div><div>That said, I’d be wary of doing anything more than that basic pair—random value from `0..<n` + convenience on `RandomAccessCollection`—at least at this point in time…I say this because I’d like to believe the stdlib will eventually gain a more-structured approach to randomness (perhaps something analogous to what C++11 picked up), and thus this feature should be kept very minimal.</div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Check if all elements in a <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Sequence</code> match a predicate (i.e. <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">!contains(!predicate)</code>)</li></ul></div></div></blockquote><div>+1, this in the stdlib is better than a million independent re-implementations.</div><div><br class=""></div><div>As a philosophical point, I’d actually prefer if `all`, `any`, `notAll`, and `notAny` (change names to suit) were all in the stdlib even if just as convenience methods defined in an extension: no point having everyone roll their own and there’s likely a minor performance advantage if such code goes in the stdlib.</div><div><br class=""></div><div>When only one “polarity” of a logical operation is available (`all` but not `none`, or `remove(where:)` but not `keep(where:)`, etc.) it seems inevitable to have occasional mismatches, and wrapping a closure in another closure just to apply `!` to it always at least “feels” wasteful. </div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class=""><code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">reduce</code> with an <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">inout</code> argument for the running value (PR for proposal here: <a href="https://github.com/apple/swift-evolution/pull/587" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;" class="">https://github.com/apple/swift-evolution/pull/587</a>)</li></ul></div></div></blockquote><div>+0.5? The performance consideration is real, but I’d hope the eventual ownership system would be able to mitigate the performance issues.</div><br class=""><blockquote type="cite" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class="">rotation of elements in a collection (deferred proposal: <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0078-rotate-algorithm.md" class="" style="box-sizing: border-box; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">https://github.com/apple/swift-evolution/blob/master/proposals/0078-rotate-algorithm.md</a>)</li></ul></div></blockquote><div>+0.5, it’s another nice thing to have in the standard library but not especially urgent. </div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Please reply here with any comments or questions on the above list, or any additions you believe are important that are missing from it.</li></ul><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class="">As this focus area is larger in scope than <code style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 11.600000381469727px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Dictionary</code>, it is likely that it will need to be broken up into multiple separate proposals. The plan is to get an initial high-level signal from this thread on which areas to put focus on. We are also looking for volunteers to put together proposals and implementations – if you're interested in helping with that, please email me off-list. High quality community implementations will significantly improve the chances of a feature making it into Swift 4. Smaller, more focussed proposals are also more likely to make it than larger ones.</p><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class="">All methods added to the standard library increase complexity, so need a strong justification to reduce the risk of API sprawl. </p></div></div></blockquote><div>One last question: what’s the right cost model for adding an associated type to a standard library protocol?</div><div><br class=""></div><div>EG: for the collection-rotation above, the `RotatedCollection` type as presently proposed would result in `RotatedCollection<Base>` returning `RotatedCollection<RotatedCollection<Base>>` from `func rotated(shiftingToStart:)`; this *could* be avoided by having `Collection`:</div><div><br class=""></div><div>- gain `associatedtype Rotation: Collection where…`</div><div>- make `func rotated(shiftingToStart index: Index) -> Rotation`</div><div>- default `Rotation = RotatedCollection<Self>`</div><div><br class=""></div><div>…and then having `RotatedCollection<Base>` make use `Rotation = RotatedCollection<Base>`.</div><div><br class=""></div><div>There’s a benefit but also a cost, and it’s never been clear *how costly* one should consider a new associated type on a stdlib protocol.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class="">When requesting additions/modifications, please keep the following questions in mind:</p><ol style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class="">Is the suggested addition a common operation that many would find useful? Can it be flexible enough to cover different needs?</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Will it encourage good practice? Might it be misused or encourage anti-patterns?</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Can the operation be composed simply from existing std lib features? Is that composition intuitive/readable? </li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Is writing the equivalent by hand hard to get right? Are there common correctness traps that this addition would help avoid?</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Is writing the equivalent by hand hard to make efficient? Are there common performance traps that this addition would help avoid?</li><li style="box-sizing: border-box; margin-top: 0.25em;" class="">Might a native implementation be able to execute more efficiently, by accessing internals, than the equivalent implementation using public APIs?</li></ol><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255);" class="">Thanks!</p><div style="box-sizing: border-box; margin-top: 0px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;" class="">Ben</div><div style="box-sizing: border-box; margin-top: 0px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;" class=""><br class=""></div><div style="box-sizing: border-box; margin-top: 0px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 14px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;" class=""><br class=""></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></blockquote></div><br class=""></body></html>