[swift-evolution] [Pitch] merge types and protocols back together with type<Type, Protocol, ...>

[Vladimir.S]

FWIW, yes, protocols available for struct are known at compile-time, but 
could be unknown at the *moment of writing* the code.

What I mean:

Step 1. I write source code:

protocol A {}
protocol B {}
struct S:A {}

func f(a: A) {
   if a is struct<S,B> {...} // I expect that S could be conformed to B
}

Step 2. I give my code to someone, who can do somewhere in his project:

extension S:B{..}



On 14.05.2016 7:06, Austin Zheng via swift-evolution wrote:
> 1. struct<SomeConcreteStruct, Protocol1, Protocol2>. In this case the
> struct<...> representation is unnecessary; the protocols that are available
> to the user are known at compile-time, and structs can't have subtypes that
> conform to additional protocols like classes can. There is an example
> marked "func boo(value: struct<SomeStruct>) /* equivalent to */ func
> boo(value: SomeStruct)"; my question is why having more than two ways to
> express the same idea makes the language better, easier to use, etc.
>