Swift: How to pass a codable type as a function input to encode or decode json

Question

I would like to make a helper function which takes input of encodable/decodable type in order to encode or decode json. I have tried

static func loadCache<T:Decodable>(fileName:String, type:T)throws->T{
        let data = try FileManager.loadCache(fileName: fileName)
        return try JSONDecoder().decode(T.self, from: data)
    }

Using the function

let products = try loadCache(fileName: Product.cacheFileName(), type: [Product])

I am getting error Type '[Product].Type' cannot conform to 'Decodable'

what is the correct way to pass this to a function Thanks

you can have to use T.type and [Product].self but you can not use files like this — Noor Ahmed Natali, Dec 20 '21 at 05:22
you can use files like this :- https://stackoverflow.com/questions/24410881/reading-in-a-json-file-using-swift — Noor Ahmed Natali, Dec 20 '21 at 05:24
@NoorAhmedNatali FileManager.loadCache is my own custom extension which generates data. I should mention that in the question i guess — Nic Wanavit, Dec 20 '21 at 08:41

score 3 · Accepted Answer · answered Dec 20 '21 at 03:58

You're very close. Your syntax is just slightly incorrect. You want to pass the type as a value, not a value of the type, so this is the signature you need:

static func loadCache<T:Decodable>(fileName:String, type: T.Type) throws -> T{
                                                           ^^^^^

Swift requires that you be very explicit about passing types as values. It requires adding .self:

let products = try loadCache(fileName: Product.cacheFileName(),
                             type: [Product].self)
                                            ^^^^^

Swift: How to pass a codable type as a function input to encode or decode json

1 Answers1