> On 9. Jul 2017, at 21:20, David Baraff <davidbar...@gmail.com> wrote: > > Nice: i hadn’t seen elementsEqual. > > (1) Why do you have to pass in “by: ==“ ? is not that the default
There are two versions: One taking an explicit predicate, and another which requires sequences of Equatable elements. As observed earlier in this thread, an array of tuples is not Equatable. > > (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? As far as I can tell from the implementation at https://github.com/apple/swift/blob/master/stdlib/public/core/SequenceAlgorithms.swift.gyb#L292 <https://github.com/apple/swift/blob/master/stdlib/public/core/SequenceAlgorithms.swift.gyb#L292> , the length is not checked a-priori, so you might want to add that to your code: 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.count == rhs.children.count && lhs.children.elementsEqual(rhs.children, by: ==) } } > > 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 >> <mailto: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 <mailto:swift-users@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-users >
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