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Json Takes Flight

· 7 min read
Hasan Abu-Rayyan
Software Engineer at Wing Cloud

Picture this: you're in the zone, crafting some spectacular code like the rock star cloud developer you are. You know that to truly harness the power of the cloud ecosystem, your system needs to be distributed. After an all-night coding spree, you've created two nifty services lovingly named service1 and service2. Now, service1 must produce a message and send it to service2. So, it's time to choose a message format standard. Given that it's 2023, XML is off the table, making JSON the clear winner.

At this point, something odd happens in your development journey. You pause to figure out how to use JSON in your chosen programming language, only to discover that you need to import a library. Sure, it's manageable, but now you have to consider the implications of using this JSON library and compare it to others. Of course, you'll make the right choice, you are a rock star, after all. However, this experience leaves you wondering: with JSON being so common, shouldn't it be built into any language designed for distributed computing?

Communication Is Key

When designing a good distributed system, several key aspects come to mind, such as fault tolerance, scalability, security, high availability, and interoperability. In this section, we'll focus on interoperability — the ability of a system to work seamlessly with other systems. This means that communication between systems must adhere to not only standardized protocols but also data formats.

Wing has been tackling the complexities of distributed computing in the cloud from various angles. One of the most notable angles is the concept of inflight functions, which serve as Wing's distributed computing primitives. These are code blocks packaged up and executed on a compute platform (i.e. AWS Lambda), playing a crucial role in Wing's vision for cloud-oriented programming. As such, it's vital to enable smooth communication between these functions, and what better way to do that than with JSON!

JSON has become the de facto standard for data interchange on the web. As a minimal, text-based format that is a subset of JavaScript, JSON is easy to read and focuses on solving a single problem: data interchange. Its simplicity and widespread adoption make JSON a clear choice for incorporating into Wing, helping us achieve the vision of a truly cloud-oriented programming language.

Introducing Wing's Json

Wing has decided to treat JSON as a first-class citizen with built-in primitives. Let's take a look at a simple example:

let j = Json {
wow: "so easy"

// Optionally we can omit the Json keyword prefix
let j = {
wow: "so easy"

That's all it takes to create a JSON object in Wing. No need to import anything!

Now, let's create an inflight function that requires a Json object as input:

bring cloud;

let b = new cloud.Bucket();

let someService = new cloud.Function(inflight (jsonString: str) => {
let message = Json.parse(jsonString);
let id = message.get("id");
let content = str.fromJson(message.get("content"));
b.put("file-${id}.txt", content);

// Test it out
test "storing a message" {
let payload = {
id: "abc123",
content: "Hello, Json!"

// retrieve object from bucket and validate content
let storedMessage = b.get("file-${str.fromJson(payload.get("id"))}.txt");
assert(storedMessage == str.fromJson(payload.get("content")));

Something noteworthy happens above when we call str.fromJson(). All fields within a Json object are of type Json, and Wing does not allow for implicit type conversions from Json to other types. Thus, we must explicitly convert the Json object to a string using the fromJson() function, which exists for all Wing primitive types.

Let's dive a little deeper and see what else Wing's Json type offers.

Converting To Structs

While Json objects are great for interoperability, they are not the best for working with data in Wing. This is because Json objects are not strongly typed. However, Wing does provide a way to convert Json objects to structs. This conversion is done by using the fromJson() function, which exists on all structs created in Wing.

Lets take a look at an example:

bring cloud;

// Struct declaration of a payload object
struct Payload {
id: str;
content: str;

// inflight function that receives json string representing a payload
let someFunction = new cloud.Function(inflight(msg: str) => {
let jsonPayload = Json.parse(msg);

// Now we can convert the json into a struct
let payload = Payload.fromJson(jsonPayload);
let content: str = payload.content;

The fromJson() function will validate the Json object at runtime and throw an error if the object does not fully match the struct definition. This is a great way to ensure that the data you are receiving is valid.

Let's add a test that will try and pass an invalid object to our inflight function:

test "json that does not match payload" {
// remember id and content are expected to be strings in our payload struct
let invalidPayload = {
id: 1,
content: false

When invoking the test above we will get the following runtime error:

│ Error: unable to parse Payload:
│ - is not of a type(s) string
│ - instance.content is not of a type(s) string

It is also worth mentioning that if the desired behavior is not to throw an exception you can also use the tryFromJson() function to get an optional type back.

Primitive Types

In line with JSON's ECMA-404 standard, Wing's Json type supports the following data primitives:

let s = Json "string";        // string
let n = Json 1; // number
let b = Json true; // boolean
let a = Json [1, 2, 3]; // array
let o = Json { a: 1, b: 2 }; // object


As with most Wing types, Json objects are immutable. This means that once a Json object is created, it cannot be modified. However, Wing does provide a way to create a mutable Json object. This is done by using the keyword MutJson instead of Json:

let j = MutJson { a: 1, b: 2 };
// We can now modify the json object elsewhere in the code
j.set("c", 3);


If you have played with Wing much, you're probably aware that nearly all container types in Wing are homogeneous. This is pretty crucial for Wing's type system, but homogeneous data doesn't work well for interoperability between systems. Take the following data for example:

let id = "abc123";
let gpa = 3.5;
let name = "John Doe";
let completed_courses = ["CS 101", "CS 102", "CS 103"];
let active = true;

Above, we have some student data, and it's clear that the data is heterogeneous and should be represented as such between systems. This is why Wing's Json type is an exception to the rule of homogeneous containers. The following is a valid Json object in Wing:

let student = Json {
id: "abc123",
gpa: 3.5,
name: "John Doe",
completed_courses: ["CS 101", "CS 102", "CS 103"],
active: true

Mission Accomplished In Progress

While we are excited about the introduction of Json into the Wing type system, we are not done yet. There are still a few features we are working on, such as removing the .get() and .set() syntax for just using the [] operator or . accessor. We also have some work to do on Json schema validation, and some other goodies which can be found in our language spec.

As always, we welcome any feedback and would love to hear from you! Come join our community discord and share your thoughts on Wing's Json support. As well check out and ⭐ our Github repo