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

[Jordan Rose]

No, both Brent and I were proposing replacing the "protocol" in "protocol<UITableViewDelegate, UITableViewDataSource>" with a different word. Brent's word was "all", as in "conforms to all of these"; mine (and JoeG's?) was "any", as in "any type conforming to these". So both of them correspond to Ceylon's "&".

(The other motivation for "any" or "Any" was by analogy with 'AnyObject' and the existing 'Any'; the latter simply becomes a short form for 'Any<>'.)

With the word "protocol" no longer in the type, we could then extend it to include a single class bound as well as protocol bounds.

Jordan


> On Feb 11, 2016, at 0:39 , Thorsten Seitz <tseitz42 at icloud.com> wrote:
> 
> Jordan, I'm not sure if I understood you correctly, do you mean to use  
> 
>    all<A, B> for intersection types (Ceylon's A & B), i.e. a type conforming to all listed types 
>    any<A, B> for union types  (Ceylon's A | B), i.e. a type conforming to any of the listed types
> 
> That would be fine, too, I think, while a bit heavier than Ceylon's syntax (though I seem to remember from another thread that there was a problem with using Ceylon's syntax in Swift, though the reason escapes me at the moment).
> 
> -Thorsten 
> 
>> Am 10.02.2016 um 18:26 schrieb Jordan Rose via swift-evolution <swift-evolution at swift.org>:
>> 
>> 
>>>> 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
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