Casting to object with Codable

All my JSON responses follow the same structure:

"success": <http code>,
"data": [

]

Where the data sent back can vary. Sometimes it can contain Users, sometimes Comments, etc. So I want to create a Codable struct that is flexible to handle the various types of objects being sent back in the data array.

Here is my current struct:

struct BasicResponse: Codable {
    let success: Int
    let data: [User]
}

As you can see, it currently only handles User data being sent back.

Then, I read the JSON data like this (through Alamofire/Moya):

var users = [User]()

let results = try JSONDecoder().decode(BasicResponse.self, from: response.data)

self.users.append(contentsOf: results.data)

How can I change my struct file to be more flexible, and how would I then cast the JSON response to the desired object?

Solution

So, without going through a lot of design cycles and straight off the top my head, I'd consider trying Swift's generic support, for example...

struct BasicResponse<DataType>: Codable where DataType: Codable {
    let success: Int
    let data: [DataType]
}

Then you just need to define the implementation of DataTypes you want to use

struct User: Codable {
    var name: String
}

And decode it...

let decoder = JSONDecoder()
let response = try decoder.decode(BasicResponse<User>.self, from: data)
print(response.data[0].name)

Now, I just threw this into a Playground and tested it with some basic data...

struct User: Codable {
    var name: String
}

struct BasicResponse<T>: Codable where T: Codable {
    let success: Int
    let data: [T]
}

let data = "{\"success\": 200, \"data\": [ { \"name\":\"hello\" }]}".data(using: .utf8)!

let decoder = JSONDecoder()
do {
    let response = try decoder.decode(BasicResponse<User>.self, from: data)
    response.data[0].name
} catch let error {
    print(error)
}

You might need to "massage" the design to better meet your needs, but it might give you a place to start