> On Jul 13, 2016, at 11:23 AM, 4 bottiglie g via swift-dev
> <[email protected]> wrote:
>
> Hi, i have asked the same question :
> Here: https://forums.developer.apple.com/message/153781#153781
> And here :
> http://stackoverflow.com/questions/38281800/array-with-associatedtype-protocol
>
> But it seams like swift doesn’t have generic protocols arrays. I am asking
> here as a last resource if it can be done yet or there is a better design.
The answer here is the same as the answer you've gotten from those other
excellent resources.
Here's the issue: Imagine that Swift supported this feature. You write this
line of code:
let event0 = events[0]
let event1 = events[1]
event0.doSomething(event1.interval)
Is this code valid? Well, who knows? `event0` and `event1` might have different
Interval types, or might not.
Java's type system does not try to protect you from this kind of mistake;
Swift's does. Unfortunately, it's not yet expressive enough to describe the
types involved. Consider this snippet:
let event = events[0]
let interval = event.interval
What's the type of `interval`? There's no way you can know for sure, really.
All you can really say is "whatever the `IntervalType` of `event` is".
There are proposals in the works to actually allow you to say
`event.IntervalType` as a type, but unfortunately they won't make Swift 3.
Until that feature is added, you have three options:
1. Fake that intended future Swift feature by writing `AnyInterval` and
`AnyEvent` type-erasing wrappers.
2. Halfway fake it by writing an `AnyEvent<IntervalType>` type-erasing wrapper.
3. Remove the associated type and require that any `Event` work with any
`Interval` (or make `Interval` a concrete type).
--
Brent Royal-Gordon
Architechies
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