[swift-users] Protocol Arrays Adding vs. Instantiating

[Team Nera]

Hi,
here are a few other ways that will compile:

af = af + [J(v:3)]
af += [J(v:4)] as [H]
af += [K(v:5)].map{ $0 as H }
af.append(K(v:6))

It does seem that "+=" does not trigger the inference of the type of the 
array literal the way "+" does. I don't know if that's a bug or one of 
those situations where you need to help the type system, the error seems 
a little bit too cryptic though.

It is by design that swift does not convert an array of concrete type to 
an array of protocol (it can take a long time), whereas single values 
are (like "w" and "x"). As I understand it, it's only because of the 
type inference on the array literal that its items are converted in the 
first two examples.

Nera



Le 25/07/2016 à 23:11, Paul Ossenbruggen via swift-users a écrit :
> Thanks to matt on stack overflow, you need to assign it to a temporary 
> to ensure the type is correct:
>
> let w : H = K(v:3)
>
> let x : H = J(v:3)
>
> af += [w]
>
> af += [x]
>
>
> Is this worthy of a bug report? Or is it inherent in the design of the 
> language?
>
> On Mon, Jul 25, 2016 at 1:02 PM, Paul Ossenbruggen <possen at gmail.com 
> <mailto:possen at gmail.com>> wrote:
>
>     In swift 3.0 beta 3, I defined a fairly simple protocol and two
>     structs that implement it, if I initialize the array when creating
>     the objects, it works, but if I try to add elements I get an error:
>
>     Cannot convert value of type '[H]' to expected argument type 'inout _'
>
>     Shouldn't this work?
>
>     protocol H {
>
>       var v : Int { get set }
>
>       func hello()
>
>     }
>
>
>     struct J : H {
>
>       var v : Int
>
>       func hello() {
>
>           print("j")
>
>       }
>
>     }
>
>
>     struct K : H {
>
>       var v : Int
>
>       func hello() {
>
>           print("k")
>
>       }
>
>     }
>
>
>     let ag:[H] =  [K(v:3), J(v:4)]
>
>     ag[0].hello()
>
>     ag[1].hello() //works
>
>
>     var af:[H] =  []
>
>     af += [K(v:3)] // does not work
>
>     af += [J(v:4)]
>
>     af[0].hello()
>
>     af[1].hello()
>
>
>
>
>
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-users/attachments/20160726/3e41411c/attachment.html>