wat.swift

import Foundation

struct StringCodingKey: CodingKey {
    var stringValue: String
    init(stringValue: String) {
        self.stringValue = stringValue
    }
    var intValue: Int? { return nil }
    init?(intValue: Int) { fatalError() }
}

@dynamicMemberLookup
struct Key {
    subscript(dynamicMember member: String) -> StringCodingKey {
        return StringCodingKey(stringValue: member)
    }
}

struct Model {
    let name: String
    let age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}

extension Model: Decodable {
    init(from decoder: Decoder) throws {
        let key = Key()
        let container = try decoder.container(keyedBy: StringCodingKey.self)
        name = try container.decode(String.self, forKey: key.name)
        age = try container.decode(Int.self, forKey: key.age)
    }
}

let j1 = """
{
"name": "Ankit",
"age": 25
}
""".data(using: .utf8)!

print(try JSONDecoder().decode(Model.self, from: j1))