[swift-evolution] [Pitch] Moving where Clauses Out Of Parameter Lists

[Haravikk]

I quite like this variation, so I’m a +1 for that.

However, I think this would be greatly helped if we could define protocol generics more like type generics like so:

	protocol Foo<Element> { … }
	func anyStringFoo(lhs:Foo<String>) { … }

But yeah, for the more complicated cases, it makes a lot of sense to relocate the where clause away from the main signature. I’d maybe still allow declarations of type though like-so:

	func anyCommonElements<T:SequenceType, U:SequenceType>(lhs:T, _ rhs:U) -> Bool
		where T.Generator.Element:Equatable, T.Generator.Element == U.Generator.Element

Perhaps allowing us the choice of doing it this way at least.

> On 6 Apr 2016, at 19:35, Pyry Jahkola via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> On 06 Apr 2016, at 21:30, Developer via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> If you've ever gotten to the point where you have a sufficiently generic interface to a thing and you need to constrain it, possibly in an extension, maybe for a generic free function or operator, you know what a pain the syntax can be for these kinds of operations.
> 
> +1 already!
> 
>> Or, if you're feeling ambitious, even
>> 
>> func anyCommonElements <T, U>
>> where T : SequenceType, U : SequenceType,
>> T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element
>> (lhs: T, _ rhs: U) -> Bool
> 
> I would actually move them as far as after everything else, and right before the definition body. For the above function that would mean:
> 
> func anyCommonElements<T, U>(lhs: T, _ rhs: U) -> Bool
>     where T : SequenceType,
>           U : SequenceType,
>           T.Generator.Element: Equatable,
>           T.Generator.Element == U.Generator.Element
> {
>     ...
> }
> 
> That would make the definition look closer to what the call site looks like.
> 
> The same would work for generic types  too:
> 
> public struct Dictionary<Key, Value>
>     where Key : Hashable
> {
>    ...
> }
> 
> — Pyry
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