Hashableでidでユニークにならない時

public class Hoge: Codable { public var id: Int public var name: String // これ追加 let creationDate: Date

public enum CodingKeys: String, CodingKey, CaseIterable {
    case id
}

// これ追加
required public init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    id = try container.decode(Int.self, forKey: .id)
    name = try container.decode(String?.self, forKey: .name)
    // ここ注意
    creationDate = try container.decode(Date.self, forKey: .creationDate)
}

}

String?.selfができる

extension Hoge: Hashable {
    public static func == (lhs: Hoge, rhs: Hoge) -> Bool {
        return lhs.id == rhs.id && lhs.creationDate == rhs.creationDate
    }

    public func hash(into hasher: inout Hasher) {
        hasher.combine(id)
        hasher.combine(creationDate)
    }
}