Use of Codable and Coding Key with JSONEncoder and JSONDecoder in Swift 4

Codable is added with Xcode 9, iOS 11 and Swift 4. Codable is used to make your data types encodable and decodable for compatibility with external representations such as JSON.

Codable use to support both encoding and decoding, declare conformance to Codable, which combines the Encodable and Decodable protocols. This process is known as making your types codable.

Let’s Take an Example with Structure of Movie, here we have defined the structure as Codable. So, We can encode and decode it easily.

We can create a object from movie like as:

The upMovie contains the name “Up” and it’s movieGenere is comedy, adventure and animation witch contains 4 rating out of 5.


JSONEncoder is an object that encodes instances of a data type as JSON objects. JSONEncoder supports the Codable object.

JSONEncoder will give us the JSON data which is used to retrieve JSON string.
Output string will be like :


JSONDecoder is an object that decodes instances of a data type from JSON objects. We can get the object back from the JSON string.

By decoding the JSONData we will receive the Movie object back. So we can get all the values which is saved in that object.

Output will be like:

Coding Key

We can change the key name to create a mapping between Swift names and JSON names, use a nested enumeration named CodingKeys within the same type that adds conformance to Codable.

Xcode Swift playground file is available at Github. Many things came with iOS 11, Xcode 9 and Swift 4.

Happy Coding 🙂