How to reference a generic Decodable struct in Swift 4

Question

I have a function that I would like to reuse and have it accept a parameter of a Decocable struct. For example, this is a simplification of my current code (assume \"MyDecodabl

Answer 1

When you want to pass a type as a parameter, you need to declare the type of the parameter as metatype. In your case, it's a generic type which needs to conform to Decodable.

So you may need to write something like this:

struct Results<Element: Decodable>: Decodable {
    let items: [Element]
}
static func getResults<Element: Decodable>(url: String, parameters: Parameters?, myStruct: Element.Type) {
    //...
        // On success REST response
        if response.result.isSuccess {

            do {
                let jsonResults = try JSONDecoder().decode(Results<Element>.self, from: response.data!)
                //success
                print(jsonResults)
            } catch {
                //Better not dispose errors silently
                print(error)
            }
        }
    //...
}

Swift says types cannot be nested in generic context, so I moved it out to the outer non-generic context.

Call it as:

getResults(url: "url", parameters: nil, myStruct: MyDecodableStruct.self)