[swift-users] Array<T> not Encodable - error at runtime, not compile time?

Itai Ferber iferber at apple.com
Thu Oct 26 12:01:47 CDT 2017

Hi Robert,

When the conditional conformance feature arrives in Swift, it will allow 
us to express `extension Array : Encodable where Element : Encodable` 
and `extension Array : Decodable where Element : Decodable`.
At the moment, this isn’t possible, so `Array` is unconditionally 
`Codable` and the failure happens at runtime. This will be a 
compile-time error in a future version of Swift.

— Itai

On 26 Oct 2017, at 9:47, Robert Nikander via swift-users wrote:

> Hi,
> This error makes perfect sense, but I’m surprised it's a runtime 
> error. I expected it at compile time. Am I doing something wrong? Is 
> this on the type system to-do list?
>   let c = JSONEncoder()
>   struct Foo { … }
>   let fs: [Foo] = [ Foo(...) ]
>   let data = try! c.encode(fs)   // Didn’t think this would compile
> The runtime error is: fatal error: Array<Foo> does not conform to 
> Encodable because Foo does not conform to Encodable.
> Rob_______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
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