[swift-evolution] Synthesizing Equatable, Hashable, and Comparable for tuple types

[Thorsten Seitz]

> Am 22.11.2017 um 06:25 schrieb Douglas Gregor via swift-evolution <swift-evolution at swift.org>:
> 
> 
> 
>>> On Nov 21, 2017, at 9:21 PM, Chris Lattner <clattner at nondot.org> wrote:
>>> 
>>> 
>>> 
>>> On Nov 21, 2017, at 7:19 PM, Douglas Gregor via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> 
>>> 
>>> Sent from my iPhone
>>> 
>>>> On Nov 21, 2017, at 3:46 PM, Tony Allevato <tony.allevato at gmail.com> wrote:
>>>> 
>>>> Does that mean that once structural types can conform to protocols, would the core team want to remove Optional as a nominal type and just use “T?”? 
>>> 
>>> Yes; at least, it’s a direction we’ve discussed a number of times. 
>>> 
>>>> Or has that ship sailed because of source compatibility and you just don’t want to introduce any new nominals that shadow structurals?
>>> 
>>> typealias Optional<T> = T?
>>> 
>>> Should address source compatibility. 
>> 
>> Or alternatively, one could decide to make the generics system *only and forever* work on nominal types, and make the syntactic sugar just be sugar for named types like Swift.Tuple, Function, and Optional.  Either design could work.
> 
> We don’t have a way to make it work for function types, though, because of parameter-passing conventions. Well, assuming we don’t invent something that allows:
> 
> 	Function<Double, inout String>
> 
> to exist in the type system. Tuple labels have a similar problem.
> 

Just throwing an idea out: what about

      Function<Double, InoutParam<String>, Param<Int>>

or

      Function<Double, Param<String, .inout>, Param<String>>

The latter assuming we had generics with value parameters (which is another common topic on this list) and defaults.
The first example might have the advantage of making use of inheritance between InoutParam and Param (which would require variance for type parameters, another common topic).

-Thorsten
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