Expected to decode Array but found a dictionary instead

Question

I was fetching data from an API returning an array but needed to replace it by an API that has \"sub levels\":

RAW:
    ETH:
        USD:
             TYPE:          


        

Answer 1

First of all the JSON does not contain any array. It's very very easy to read JSON. There are only 2 (two!) collection types, array [] and dictionary {}. As you can see there are no square brackets at all in the JSON string.

Any (sub)dictionary {} has to be decoded to its own type, so it's supposed to be

struct Root : Decodable {
    private enum CodingKeys : String, CodingKey { case raw = "RAW" }
    let raw : RAW
}

struct RAW : Decodable {
    private enum CodingKeys : String, CodingKey { case eth = "ETH" }
    let eth : ETH
}

struct ETH : Decodable {
    private enum CodingKeys : String, CodingKey { case usd = "USD" }
    let usd : USD
}

struct USD : Decodable {

    private enum CodingKeys : String, CodingKey {
        case type = "TYPE"
        case market = "MARKET"
        case price = "PRICE"
        case percentChange24h = "CHANGEPCT24HOUR"
    }
    let type : String
    let market : String
    let price : Double
    let percentChange24h : Double
}

To decode the JSON and and print percentChange24h you have to write

 let result = try JSONDecoder().decode(Root.self, from: data)
 print("percentChange24h", result.raw.eth.usd.percentChange24h)