[swift-users] is this a defect in equatable for swift tuples?

[Jens Persson]

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
            })
    }
}


On Sun, Jul 9, 2017 at 8:44 PM, David Sweeris <davesweeris at mac.com> wrote:

>
> On Jul 9, 2017, at 10:06, David Baraff via swift-users <
> swift-users at swift.org> wrote:
>
>
> On Jul 9, 2017, at 8:27 AM, Jens Persson <jens at 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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