[swift-evolution] Specify type of a delegate which conforms to a protocol

[Jordan Rose]

> On Feb 10, 2016, at 5:00 , Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> So, I definitely think there is room for improvement here… how about recycling the inheritance syntax?
>> 
>> let controller: (UIViewController, UITableViewDatasource)
> 
> This declares a tuple containing a UIViewController and a UITableViewDataSource.
> 
>> I added the braces because it would be really when you add the question mark for an optional value; an alternative for this case would be
>> 
>> let controller: Optional<UIViewController, UITableViewDatasource>
> 
> This attempts to declare an optional with two generic types, which doesn't work because Optional only has one type parameter. (But other types, like Dictionary, *do* take two type parameters.)
> 
> Swift does already have a syntax for declaring that a type must conform to two (or more!) protocols:
> 
> 	let controller: protocol<UITableViewDataSource, UITableViewDelegate>
> 
> I think this could probably be extended to support one class type as well, perhaps with a new name:
> 
> 	let controller: all<UIViewController, UITableViewDataSource>

We've been calling it "any" or "Any" (as in "any instance that is-a UIViewController and is-a UITableViewDataSource"), but I think this is the direction we've been talking about over here.

(Not that syntax bikeshedding can't still be useful.)

Jordan