title: Swift Decodable can't decode with single root element
body: <p>I'm having hard time decoding with swift Decodable protocol. I have a REST API which returns the following JSON</p>
  
  <pre class="lang-js prettyprint-override"><code>{
    data: [
      {
        id: 17,
        status: "published",
        created_by: {
          id: 1
        },
        created_on: "2020-01-13 17:38:31",
        title: "Lorem ipsum dolor sit amet, consectetur adi",
        content: "&lt;p&gt;Mauris id ligula et metus porta rutrum vitae ac mi. Mauris rhoncus sagittis facilisis. Cras suscipit nisi quis risus lacinia dictum. Morbi porttitor, est sodales tristique interdum, erat leo consequat lorem, in cursus metus est eget felis. Cras a sapien massa. Sed tincidunt fermentum imperdiet. Ut velit diam, interdum sit amet lectus vitae, tristiq&lt;/p&gt;",
        featured_image: {
          data: {
            full_url: "https://example.com/originals/14eefd0d-93fc-44f6-84a5-7cf86a2e83fc.jpg",
            url: "/uploads/abc/originals/14eefd0d-93fc-44f6-84a5-7cf86a2e83fc.jpg",
            thumbnails: [...],
            embed: null
          }
        },
        source: null,
        is_featured: true
      }
    ]
  }
  </code></pre>
  
  <p>And the structure of my model</p>
  
  <pre class="lang-swift prettyprint-override"><code>struct PostRoot:Decodable {
      let data:[Post]
  }
  
  struct Post: Decodable {
      let id:Int
      let title:String
      let created_on:String
      let content:String
      let source:String
      let f_image:FeaturedImage
  }
  
  struct FeaturedImage: Decodable {
      let data:ImagePath
  }
  
  struct ImagePath: Decodable{
      let full_url:String
  }
  
  // Only included the decoding part, not the request part
  
  if let d = data {
    let decodedLists = try JSONDecoder().decode(PostRoot.self, from: d)
    print(decodedLists)
  }
  </code></pre>
  
  <p>After getting the response from my server, the decoding process always ends up in error, do I have to map each and every keys ? what am I missing here ?</p>
  
  <p>This is the error:</p>
  
  <blockquote>
    <p>Error: keyNotFound(CodingKeys(stringValue: "f_image", intValue: nil), Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "data", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "No value associated with key CodingKeys(stringValue: \"f_image\", intValue: nil) (\"f_image\").", underlyingError: nil))</p>
  </blockquote>