title: does not conform to protocol Decodable / Codable
body: <p>I'm using the following struct:</p>
  
  <pre><code>struct Item : Codable {
  
      var category:String
      var birthDate:Date
      var switch:Bool
      var weightNew: [Weight]
      var weightOld: Array&lt;Double&gt;
      var createdAt:Date
      var itemIdentifier:UUID
      var completed:Bool
  
      func saveItem() {
          DataManager.save(self, with: itemIdentifier.uuidString)
      }
  
      func deleteItem() { DataManager.delete(itemIdentifier.uuidString)
      }
  
      mutating func markAsCompleted() {
          self.completed = true
          DataManager.save(self, with: itemIdentifier.uuidString)
      }
  
  }
  </code></pre>
  
  <p>And for weight:</p>
  
  <pre><code>struct Weight {
      var day:Int
      var weight:Double
      var type:Bool
  }
  </code></pre>
  
  <p>After changing weightOld to weightNew I get two errors:
  - Type 'Item' does not conform to protocol 'Decodable'
  - Type 'Item' does not conform to protocol 'Codable'</p>
  
  <p>If I leave out 'var weightNew: [Weight]' it works. Don't know what is happening and how to solve it... Help is appreciated. </p>