> On 9. Jul 2017, at 21:00, Jens Persson via swift-users
> <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
>
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