[swift-evolution] [Pitch] Make Optional, Array, and Dictionary conditionally Equatable

[Thorsten Seitz]

+1

-Thorsten


> Am 22.11.2017 um 18:48 schrieb Chris Lattner via swift-evolution <swift-evolution at swift.org>:
> 
> IMO this is obvious and you should put it in.
> 
> The process serves a purpose: to ensure the evolution of the language is going in the right place, both directionally in an details.  It is obvious that we’re going to take this, and the details are clear, therefore doing an evolution cycle for this would just waste everyone’s time.
> 
> That said, when you get to less obvious introductions and start doing more major consolidation and simplification of the stdlib, those changes may be worthy of discussion to ensure the details are right.
> 
> -Chris
> 
>> On Nov 21, 2017, at 10:51 PM, Douglas Gregor via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> Hi all,
>> 
>> We’re having a bit of a debate <https://github.com/apple/swift/pull/12910> over the question of whether SE-0143 “Conditional Conformances” <https://github.com/apple/swift-evolution/blob/master/proposals/0143-conditional-conformances.md> actually proposes any standard library changes at all, or whether they should all be brought up separately. So, I’ll pitch the pieces that I’d love to put into 4.1 to see if they’re as obvious as I think they should be :)
>> 
>> Proposal: make Optional, Array, ArraySlice, ContiguousArray, and Dictionary conform to Equatable when their type parameters are Equatable (and Set always conform to Equatable). Specifically, add to the standard library:
>> 
>> 	extension Optional: Equatable where Wrapped: Equatable { /*== already exists */ }
>> 	extension Array: Equatable where Element: Equatable { /*== already exists */ }
>> 	extension ArraySlice: Equatable where Element: Equatable { /*== already exists */ }
>> 	extension ContiguousArray: Equatable where Element: Equatable { /*== already exists */ }
>> 	extension Dictionary: Equatable where Value: Equatable { /*== already exists */ }
>> 	extension Set: Equatable { /*== already exists */ }
>> 
>> Motivation: we need these for ==/!= to properly compose. It’s a highly-requested feature and an obvious “first use” of conditional conformances for the standard library that is unlikely to break any code.
>> 
>> Implementation: https://github.com/apple/swift/pull/13046 <https://github.com/apple/swift/pull/13046>
>> 
>> Thoughts?
>> 
>> 
>> 	- Doug
>> 
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