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@gmail.com > <mailto:possen@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()
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