[swift-users] [swift-evolution] Request for information about constrained protocol inheritance

[Alex Martini]

Since you mentioned not finding documentation, here's the new section in "The Swift Programming Language":

Associated Types with a Generic Where Clause

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html#//apple_ref/doc/uid/TP40014097-CH26-ID557

> On Jul 4, 2017, at 10:53 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Replying to swift-users as well, as it's probably the more appropriate forum.
> 
> SE-0142 (Permit where clauses to constrain associated types) is what brought about this feature. It is now used in the standard library.
> 
> 
> On Wed, Jul 5, 2017 at 00:26 Jens Persson via swift-evolution <swift-evolution at swift.org> wrote:
> The following compiles in Swift 4 (but not in Swift 3.1):
> 
> protocol P1 {
>     associatedtype A
> }
> protocol P2 : P1 where A == Int {
> }
> 
> I've not been able to find any proposal, discussion or documentation mentioning it so any pointers to such would be greatly appreciated.
> 
> Also, is this new feature used somewhere in the std lib?
> 
> /Jens
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