[swift-evolution] Either protocol syntax

[Matthew Johnson]

> 
> On Feb 2, 2017, at 3:26 PM, Rex Fenley via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Hello, I believe there was some discussion about this quite awhile ago. I was wondering if there's any interest in including a protocol 'or' type that would be the intersection of two protocols. This could be really useful in situations where a framework that the user has no control over implements a portion of some often used protocol. Such as specialized collections from an Database framework that don't implement RangeReplaceableCollection but have a set of methods that are equivalent. The user can then implement a protocol that is the intersection of those set of methods and not duplicate code.

If the specialized collection in the database framework already provides functionality equivalent to `RangeReplaceableCollection` what you really want to do is just provide the conformance you’re looking for in an extension:

extension SpecializedDatabaseCollection: RangeReplaceableCollection {
   // if necessary, provide forwarding wrappers where the member names don’t match up.
}

But in a case like this the framework itself really should provide this conformance out of the box.  If they didn’t, maybe there is a good reason so you would want to find out why it wasn’t provided.

Is there something you’re hoping to do that you can’t solve by simply extending the framework types?

> 
> Simplified example:
> 
> protocol Animal {
>     var hasEars: Bool { get }
>     func grow()
> }
> 
> protocol Plant {
>     var isGreen: Bool { get }
>     func grow()
> }
> 
> protocol LivingThing = Plant | Animal // or a different syntax
> 
> LivingThing's is as follows
> {
>     func grow()
> }
> 
> -- 
> Rex Fenley  |  IOS DEVELOPER
> 
> 
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