Xcode warning: Immutable property will not be decoded because it is declared with an initial value which cannot be overwritten

Question

Running Xcode 12, my Swift 5 Xcode project now has warnings whenever a Decodable or Codable type declares a let constant with an initial v

Answer 1

Solution: define an explicit CodingKeys enum to prevent id from decoded. For example,

struct Course: Identifiable, Decodable {
  let id = UUID()
  let name: String

  private enum CodingKeys: String, CodingKey {
    case name
  }
  
  init(name: String) { self.name = name }
  init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    let name = try container.decodeIfPresent(String.self, forKey: .name)
    self.name = name ?? "default-name"
  }
}