title: Swift 4 decodable with unknown dynamic keys
body: <p>I have the following JSON</p>
  
  <pre><code>{"DynamicKey":6410,"Meta":{"name":"","page":""}}
  </code></pre>
  
  <p>DynamicKey is unknown at compile time.I'm trying to find a reference how to 
  parse this struct using decodable.</p>
  
  <pre><code>public struct MyStruct: Decodable {
      public let unknown: Double
      public let meta: [String: String]
  
      private enum CodingKeys: String, CodingKey {
          case meta = "Meta"
      }
  }
  </code></pre>
  
  <p>Any ideas?</p>