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

[David Sweeris]

> 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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