What is Decodable Swift? Encodable and Decodable are the powerful features in swift standard library to handle data encoding and decoding tasks easily. Many types in swift standard library and Foundation framework such as Date, URL are Codable out of the box which makes Encodable and Decodable compelling for data serialization/deserialization.
What is a decodable type?
A type that can decode itself from an external representation. Creates a new instance by decoding from the given decoder. Required. Default implementation provided. Conforms when Element conforms to Decodable.
How does the Swift decoding process work?
As you might expect, the overall decoding process works like the reverse of the encoding process: Dispatch to each type’s Decodable initializer to reconstruct a series of Swift instances Let’s start with a JSON string representing an array of integers and turn that into some Data:
What is a decodable container?
This type has to itself be Decodable. container is the unkeyed container, an array of anything [Any]. Now that we have our container with the elements to decode and we know the type of the elements, it’s time to loop:
How do I decode a JSON array in Swift?
First we spin up a _JSONDecoder, the private class that conforms to Decoder and contains JSON-specific logic. Remember T is the generic parameter for the Swift equivalent to topLevel; in this case, it’s [Int] aka Array<Int> so we can decode our array [0, 1, 2].
What is decode in Swift?
The three-step process to decode JSON data in Swift Perform a network request to fetch the data. Feed the data you receive to a JSONDecoder instance. Map the JSON data to your model types by making them conform to the Decodable protocol.
What is Encodable and Decodable?
Codable means they can be decoded from and encoded into another representation. Decodable means it can be decoded, but not encoded. And encodable is the opposite of that. Follow this answer to receive notifications.
What is encoding Swift?
The Swift standard library defines a standardized approach to data encoding and decoding. You adopt this approach by implementing the Encodable and Decodable protocols on your custom types.
What is Encodable?
A type that can encode itself to an external representation.
What is Decodable in Swift iOS?
Swift can generate code to decode JSON into these structs because Product 's properties are all Decodable . This means that Response 's properties are also all Decodable since [Product] is Decodable . Remember, arrays are Decodable (or Codable ) as long as their Element is Decodable (or Codable ).
What does the term Decodable mean?
Decodable definition Able to be read using a certain set of reading knowledge. Decodable books are sold in packs, with more letter combinations appearing in each successive book. adjective. (information theory) Of a code, having a non-singular extension; being a lossless encoding. adjective.
What is Decodable in iOS?
A type that can decode itself from an external representation. iOS 8.0+
What is encoding and decoding in Swift?
But before you can do that, you need to convert the data to a suitable format through a process called encoding or serialization. You'll also need to convert the saved data sent over the network to a suitable format before using it in your app. This reverse process is called decoding or deserialization.
What is serialization in Swift?
2019. Serialization is a process of converting your instances to another representation, like a string or a stream of bytes. The reverse process of turning the data into an instance is called decoding, or deserialization.
What does Codable do in Swift?
Codable allows you to insert an additional clarifying stage into the process of decoding data into a Swift object. This stage is the “parsed object,” whose properties and keys match up directly to the data, but whose types have been decoded into Swift objects.
What is Codable data?
What is Codable? Codable is to convert the JSON data object to an actual Swift class or struct and vice versa. It's usually used when the case you wanna retrieve or parse JSON data from the server like the APIs.
How do you use Codable in Swift 5?
Encoding Swift Objects as JSON with CodableFirst, you create a User object and assign some values to its properties.Then, you use encode(_:) to encode the user object to a JSON Data object.Finally, you convert the Data object to String and print it out.
Basics
If you haven’t seen it already, I suggest you to watch the related WWDC session (the Codable part starts past 23 minutes).
What the Compiler Does Without Telling Us
If we look at the Decodable documentation, we see that the protocol requires the implementation of a init (from: Decoder) method.
Conforming to Decodable
All of the above is great and just works™ as long as all we need to parse is a subsets of primitives (strings, numbers, bools, etc) or other structures that conform to the Decodable protocol.
Going further (More Playgrounds!)
Now that our Swifter struct conforms to Decodable, any other struct/class/etc that contains such data can automatically decode Swifter for free. For example:
Before Departing
In all probability, during your first Decodable implementations, something will go wrong: maybe it’s a key mismatch, maybe it’s a type mismatch, etc.
Conclusions
I was really looking forward to this new Swift 4 feature and I’m very happy with its implementation. Time to drop all those custom JSON parsers!
Dictionary 101
Swift dictionaries are a generic collection of key-value elements, where the Key type needs to conform to Hashable (for performance reasons), and the Value type has no restrictions.
The surprise
Let's imagine that we're building a small app where each model has different names in different languages, all to be displayed to the user at will.
Four solutions
At this point we know that Swift dictionaries will encode into/decode from json dictionaries only when its key is either a String or a Int, how can we overcome this in our example? Let's see a few solutions.
Conclusions
The introduction of Codable in Swift was a blessing: despite having a few shortcoming here and there, it's also flexible enough for us to extend it and make it work for our needs.
Decoder
As with encoding, JSONDecoder is the class with a friendly interface and handy decode () method called above. What does that method look like?
JSON Decoder
We instantiated a _JSONDecoder and passed it into the top-level container’s initializer. What’s inside the _JSONDecoder?
The Closing Brace
We made it! All the way from a JSON string, through decodable and decoders, to unkeyed containers, to loops, to individual values.