On 14.05.2016 21:20, Austin Zheng wrote:
Yes, this is theoretically possible, but why is it useful? (I am genuinely curious.)
I just showing that we *can* invent the situation when checking for struct<Struct,Protocol> have a sense. Not more, not less. I'm not going to discuss if that can have any (or never can have at all) useful intention.
If the intention is to allow B to be a user-defined extension point for T, this goes back to the core team's arguments (in the thread about optional protocol requirements) about why having checking for conformance to some requirement at the use site is a suboptimal idea. If the intention is to make the type system as expressive as possible, the core team has already ruled out a number of features (user-defined variance on generics, generic protocols) because they don't believe in their general applicability. Austin On Sat, May 14, 2016 at 11:13 AM, Vladimir.S <sva...@gmail.com <mailto:sva...@gmail.com>> wrote: 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.
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