Any idea why I'm receiving this error message in the console!!! Initialization of immutable value 'container', Help!

import Foundation

let json = """
{
    "name": "Pasan",
    "id": 1,
    "role": "Teacher"
}

//Conversting string literal into a data object with utf8
""".data(using: .utf8)!

struct Employee: Codable
{
    let name: String
    let id: Int
    let role: String

    enum CodingKeys: String, CodingKey
    {
        //Providing a raw value
        case name = "name"
        case id = "id"
        case role = "role"

    }

    init (from decoder: Decoder) throws
    {
        let container = try decoder.container(keyedBy: CodingKeys.self)



        self.name = try container.decode(String.self, forKey: .name)
        self.id = try container.decode(Int.self, forKey: .id)
        self.role = try container.decode(String.self, forKey: .role)

    }
}

//We need a decoder to handle decoding the JSON, parsing it and assigning values.
let decoder = JSONDecoder()

//Creating an instance of JSONDecoder
let employee = try! decoder.decode(Employee.self, from: json)

employee.name
employee.role