Nice: i hadn’t seen elementsEqual. (1) Why do you have to pass in “by: ==“ ? is not that the default
(2) not a big deal, but if the sequence type’s length can be determined a priori (e.g. in the case of an Array, or perhaps a Collection if that has a count member, haven’t checked) does the elementsEqual function short circuit by first checking that the lengths are equal before beginning the loop? But again, that’s a great one to know. > On Jul 9, 2017, at 12:14 PM, Martin R via swift-users <swift-users@swift.org> > wrote: > > >> On 9. Jul 2017, at 21:00, Jens Persson via swift-users >> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >> >> Since Array has .elementsEqual, another workaround (until conditional >> conformance) is: >> >> class Tree : Equatable { >> let rootData:Int >> let children:[(String, Tree)] >> >> init(rootData: Int, children: [(String, Tree)]) { >> self.rootData = rootData >> self.children = children >> } >> static public func ==(_ lhs:Tree, _ rhs:Tree) -> Bool { >> return lhs.rootData == rhs.rootData && >> lhs.children.elementsEqual(rhs.children, by: { (a: (String, >> Tree), b: (String, Tree)) -> Bool in >> return a.0 == b.0 && a.1 == b.1 >> }) >> } >> } > > > Slightly simpler (since == is already defined for the tuples): > > class Tree : Equatable { > let rootData:Int = 0 > let children:[(String, Tree)] = [] > > static public func ==(_ lhs:Tree, _ rhs:Tree) -> Bool { > return lhs.rootData == rhs.rootData && > lhs.children.elementsEqual(rhs.children, by: ==) > } > } > > >> >> >> On Sun, Jul 9, 2017 at 8:44 PM, David Sweeris <daveswee...@mac.com >> <mailto:daveswee...@mac.com>> wrote: >> >> On Jul 9, 2017, at 10:06, David Baraff via swift-users >> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >> >>> >>>> On Jul 9, 2017, at 8:27 AM, Jens Persson <j...@bitcycle.com >>>> <mailto:j...@bitcycle.com>> wrote: >>>> >>>> (Also, note that your implementation of == uses lhs === rhs thus will only >>>> return true when lhs and rhs are the same instance of SomeClass.) >>> Of course — i threw that in just to make a simple example. >>> >>> Followup question: what I really wanted to write was an == operator for a >>> tree: >>> >>> // silly tree, useful for nothing >>> class Tree : Equatable { >>> let rootData:Int >>> let children:[(String, Tree)] >>> >>> static public func ==(_ lhs:Tree, _ rhs:Tree) { >>> return lhs.rootData == rhs.rootData && >>> lhs.children == rhs.children // sadly, this doesn’t >>> compile >>> } >>> } >> >> Right, the `==` func is *defined* for 2-element tuples where both elements >> conform to `Equatable`, but that tuple type doesn't itself *conform* to >> `Equatable`. So the`==` func that's defined on "Array where Element: >> Equatable" can't see it. >> >> We'd need both "conditional conformance" and "tuple conformance" in order >> for that to Just Work. >> >> - Dave Sweeris >> >> _______________________________________________ >> swift-users mailing list >> swift-users@swift.org <mailto:swift-users@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-users >> <https://lists.swift.org/mailman/listinfo/swift-users> > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users
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