Hi Doug,
I've read the discussion about moving the where clause to the right of
declarations (which I full-heartedly approve) but I don't see how it would have
any impact on the syntax of associated types requirements.
David
> On 12 Apr 2016, at 19:07, Douglas Gregor via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>
>>> On Apr 11, 2016, at 1:01 AM, Jacob Bandes-Storch via swift-evolution
>>> <swift-evolution@swift.org> wrote:
>>>
>>> Doug wrote this in the Completing Generics manifesto, under "Minor
>>> extensions":
>>>
>>
>>> *Arbitrary requirements in protocols
>>>
>>> Currently, a new protocol can inherit from other protocols, introduce new
>>> associated types, and add new conformance constraints to associated types
>>> (by redeclaring an associated type from an inherited protocol). However,
>>> one cannot express more general constraints. Building on the example from
>>> “Recursive protocol constraints”, we really want the element type of a
>>> Sequence’s SubSequence to be the same as the element type of the Sequence,
>>> e.g.,
>>>
>>> protocol Sequence {
>>> associatedtype Iterator : IteratorProtocol
>>> …
>>> associatedtype SubSequence : Sequence where
>>> SubSequence.Iterator.Element == Iterator.Element
>>> }
>>
>>
>> +1.
>>
>> To make it into Swift 3, would this feature require a proposal of its own?
>
> Yes. Also, be wary that the syntax above potentially conflicts with the
> syntax discussed as "moving the where clauses”:
>
>
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/13886/focus=14058
>
>
>> How feasible would it be to implement on top of the current system?
>
> Definitely! The archetype builder would need to learn to check these extra
> where clauses, and one would need to be sure that the constraint solver is
> picking them up as well.
>
> - Doug
>
>
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