[swift-users] still wrestling with a type conversion problem

[David Baraff]

> On Jul 4, 2017, at 5:48 PM, Jacob Bandes-Storch <jtbandes at gmail.com> wrote:
> 
> On Tue, Jul 4, 2017 at 7:21 AM, David Baraff <davidbaraff at gmail.com <mailto:davidbaraff at gmail.com>> wrote:
> 
>     func decoded(_ input: Any) -> Set {
>         if let listVal = input as? [Set.Element] {
>             return Set(listVal)
>         }
>         return self
>     }
> 
> 
> This looks a little weird — what is `self` here? It might be more appropriate to use a `static func` or even a failable `init?`.

I figure out how to do this right.  Something like:

protocol DecodableFromAny {
    static func fromAny(_ payload:Any) -> Self?
}

extension Array : DecodableFromAny {
    static func fromAny(_ payload: Any) -> Array? {
        if let x = payload as? [Array.Element] {
            return x
        }
        return nil
    }
}

func decodeMe<T>(_ payload:Any) -> T? {
    if  let dt = T.self as? DecodableFromAny {
        return type(of: dt).fromAny(payload) as! T
    } else {
        return payload as? T
    }
}

I got tripped up not realizing I could cast “T.self” to the protocol, and then call it once i invoked type(of:) on that.  much much nicer this way.

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