Codable protocol for encoding/decoding in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Codable protocol in Swift?

The Codable protocol is a combination of Encodable and Decodable. It allows Swift types to be easily converted to and from external representations like JSON or Property Lists.

beginner

How do you make a Swift struct conform to Codable?

You add Codable to the struct's declaration. For example: <br>

struct User: Codable {<br>  var name: String<br>  var age: Int<br>}

intermediate

What are the two main functions provided by Encodable and Decodable?

Encodable provides encode(to encoder: Encoder) to convert data to an external format.<br>Decodable provides init(from decoder: Decoder) to create an instance from external data.

beginner

What Swift class is commonly used to encode and decode JSON data?

The <code>JSONEncoder</code> class is used to encode Swift types to JSON.<br>The <code>JSONDecoder</code> class is used to decode JSON data back into Swift types.

intermediate

How can you customize the keys used during encoding and decoding?

You define an enum called CodingKeys inside your type that conforms to CodingKey. This enum maps your property names to the keys used in the encoded data.

Which protocol must a Swift type conform to for automatic JSON encoding and decoding?

A Codable

B Serializable

C JSONRepresentable

D EncodableOnly

The Codable protocol combines Encodable and Decodable for easy JSON encoding and decoding.

What does JSONDecoder do?

A Converts Swift objects to JSON data

B Converts JSON data to Swift objects

C Validates JSON syntax

D Encrypts JSON data

JSONDecoder converts JSON data into Swift objects.

How do you specify custom keys for encoding properties?

A By overriding <code>encode(to:)</code> only

B By using <code>JSONEncoder.keyMapping</code>

C By renaming the properties

D By defining a <code>CodingKeys</code> enum

Defining a CodingKeys enum lets you map property names to custom keys.

If a struct conforms to Codable, what must you do to encode it to JSON?

A Manually write JSON strings

B Call <code>encode()</code> on the struct directly

C Call <code>JSONEncoder().encode()</code> with the struct instance

D Use <code>JSONSerialization</code> only

Use JSONEncoder().encode() to convert the struct to JSON data.

What happens if a property is missing in the JSON when decoding?

A The property is set to nil if optional

B Decoding fails with an error

C The property is ignored silently

D The decoder fills it with default values automatically

If the property is optional, it becomes nil; otherwise decoding fails.

Explain how the Codable protocol helps in encoding and decoding data in Swift.

Think about how you turn Swift objects into JSON and back.

Describe how to customize the keys used when encoding a Swift struct to JSON.

It's about telling Swift which names to use in JSON.