2201.8.0 (Swan Lake)

Overview of Ballerina Swan Lake Update 8 (2201.8.0)

Swan Lake Update 8 (2201.8.0) is the eighth update release of Ballerina Swan Lake, and it includes a new set of features and significant improvements to the compiler, runtime, Ballerina library, and developer tooling. It is based on the 2023R1 version of the Language Specification.

Update Ballerina

Update your current Ballerina installation directly to 2201.8.0 using the Ballerina Update Tool as follows.

  1. Run bal update to get the latest version of the Update Tool.
  2. Run bal dist update to update to this latest distribution.

Install Ballerina

If you have not installed Ballerina, download the installers to install.

Language updates

New features

Introduction of list constants

The language now supports list constants. You can declare a constant variable using a list constructor as shown below.

const int[] ERROR_CODES = [404, 500, 503];
const ERROR_MESSAGES = ["Not Found", "Internal Server Error", "Service Unavailable"];

Also, you can declare a list constant using a byte array literal as shown below.

const byte[] data16 = base16 `55 EE 66`;
const data64 = base64 `ABCD pqrs`;


Make async-send an action

Reclassified async-send from a statement to an action in alignment with the Ballerina specification.

The following case is now supported.

public function main() {
    worker w1 {
        () res = 5 -> w2;
    worker w2 {
        int val = <- w1;

Bug fixes

To view bug fixes, see the GitHub milestone for Swan Lake Update 8 (2201.8.0).

Runtime updates

New features

New runtime Java APIs

Introduced the Type getImpliedType(Type) API in the io.ballerina.runtime.api.utils.TypeUtils class to recursively resolve type-reference types (to get referred types) and/or intersection types (to get effective types).

// `getImpliedType` on type A returns a `BArrayType`. This is achieved by first retrieving the 
// referred type of the type reference type, which will be an intersection type, and then, 
// retrieving the effective type of the intersection type.
type A int[] & readonly;

Ballerina Profiler (experimental)

Introduced the CLI command below, which runs a Ballerina package and does a CPU profile of it during runtime.

$ bal profile

For example, if you run the above command in the root directory of a Ballerina package, it generates a flame graph that shows the time taken to execute each function. The output is given by the ProfilerOutput.html file, which can be opened using a web browser.

Note: This is an experimental feature, which supports only a limited set of functionality.

For more information, see Ballerina Profiler.


Java 17 support

The Java 11 Long term Support (LTS) active support will end in September 2023. Therefore, the jBallerina runtime is now upgraded to support Java 17 LTS, which is the latest long-term support release of the Java SE platform.

Note: Users will not have an impact on the Java version upgrade except for the following. If you are specifically using Java 11 to run Ballerina programs, you would have to switch to Java 17. However, the Ballerina interoperability implementation will have an impact on Java 17 support due to any incompatible changes. As an example, Java 17 will have some restrictions on using Java reflections with internal Java packages.

For more information, see the Java 17 release notes.

Support large list and mapping constructors

The number of members supported in a list constructor expression and the number of fields supported in a mapping constructor expression have been increased to create new array, tuple, map, and record values that are larger.

For example, the following array constructor is now supported.

// Array with 10000 elements. Middle elements are not shown and replaced with `...`.
int[] array = [1, 2, 3, ..., 9998, 9999, 10000];

Intersection type support in runtime Java APIs

The following runtime APIs are now modified to return an intersection type rather than returning the effective type of the intersection.

Runtime APIJava class
getParameters (The Parameter.type field can be an intersection type.)io.ballerina.runtime.api.types.FunctionType

For example, if an intersection type is defined in the following way,

type ReadonlyIntArray readonly & int[];
ReadonlyIntArray array = [1, 2, 3, 4];

the results of the runtime API calls will be as follows.

Runtime API callResult
array.getType()This will return an IntersectionType instead of ArrayType.
getDescribingType() on ReadonlyIntArray typeThis will return an IntersectionType instead of ArrayType.
getImpliedType() on received IntersectionType typeThis will return an ArrayType.

Bug fixes

To view bug fixes, see the GitHub milestone for Swan Lake Update 8 (2201.8.0).

Ballerina library updates

New features

mqtt package

  • Introduced the mqtt package, which provides an implementation to interact with message brokers using the MQTT protocol.

java.jms package

  • Introduced the java.jms package, which provides an implementation to interact with message brokers using the JMS protocol.

graphql package

  • Introduced the DataLoader functionality as shown in the example below.

    import ballerina/graphql;
    import ballerina/graphql.dataloader;
    import ballerina/http;
    public type Book record {|
        int id;
        string title;
    type BookRow record {|
        readonly int id;
        string title;
        int author;
    type AuthorRow record {|
        readonly int id;
        string name;
    final readonly & table<AuthorRow> key(id) authorTable = table [
        {id: 1, name: "J.K. Rowling"},
        {id: 2, name: "Stephen King"}
    final readonly & table<BookRow> key(id) bookTable = table [
        {id: 1, title: "Harry Potter and the Sorcerer's Stone", author: 1},
        {id: 2, title: "The Shining", author: 2},
        {id: 3, title: "Harry Potter and the Chamber of Secrets", author: 1},
        {id: 4, title: "It", author: 2},
        {id: 5, title: "Harry Potter and the Prisoner of Azkaban", author: 1},
        {id: 6, title: "The Stand", author: 2}
    // Implement the batching logic.
    isolated function bookLoaderFunction(readonly & anydata[] ids) returns BookRow[][]|error {
        final readonly & int[] keys = check ids.ensureType();
        return keys.'map(isolated function(readonly & int key) returns BookRow[] {
            return bookTable.'filter(book => book.author == key).toArray();
    @graphql:ServiceConfig {
        contextInit: isolated function(http:RequestContext requestContext, http:Request request) 
        returns graphql:Context {
            graphql:Context ctx = new;
            // Register the dataloader with the context using a unique name.
            ctx.registerDataLoader("bookLoader", new dataloader:DefaultDataLoader(bookLoaderFunction));
            return ctx;
    service /graphql on new graphql:Listener(9090) {
        resource function get authors() returns Author[] {
            return from AuthorRow authorRow in authorTable
                select new (authorRow);
    public isolated distinct service class Author {
        private final readonly & AuthorRow author;
        isolated function init(readonly & AuthorRow author) {
            self.author = author;
        isolated resource function get name() returns string {
            return self.author.name;
        // Define a prefetch function.
        isolated function preBooks(graphql:Context ctx) {
            dataloader:DataLoader bookLoader = ctx.getDataLoader("bookLoader");
            // Add the primary key of the data to be fetched to the dataloader.
        isolated resource function get books(graphql:Context ctx) returns Book[]|error {
            dataloader:DataLoader bookLoader = ctx.getDataLoader("bookLoader");
            // Obtain the data from the dataloader using the primary key of the data.
            BookRow[] bookRows = check bookLoader.get(self.author.id);
            return from BookRow bookRow in bookRows
                select {id: bookRow.id, title: bookRow.title};


graphql package

  • Deprecated the executeWithType() method of the graphql:Client.


graphql package

  • Added support for the @deprecated directive in output objects defined using record types.
  • Added support for printing the GraphiQL URL to stdout.
  • Added support for generating a subgraph SDL schema at compile time.

log package

  • Made adjustments to the behavior of the log print functions when an error object is provided for the error key. Updated the previous version, which displayed only the error message to provide more detailed information, including both the error message and the stack trace for the current error as well as any underlying errors that contributed to the current error.
  • Removed the extra space that was printed between the key and value when printing in the LogFMT format.

persist package

  • Added support for printing an executed SQL statement as debug logs.
  • Added support for executing native queries in SQL databases.
  • Improved advanced filter query support for SQL databases to filter at the database level.

Bug fixes

To view bug fixes, see the GitHub milestone for Swan Lake Update 8 (2201.8.0).

Developer tools updates

New features

Language Server

  • Added custom completions for HTTP services.


  • Added a new bal tool command to manage tools that extend the functionality of the CLI. Tools can be pulled from Ballerina Central and are managed using the bal tool command. For more information, see CLI commands.

OpenAPI tool

  • Added support to generate Ballerina client and service declarations from OpenAPI v3.1.x definitions.


Language Server

  • Improved the search to suggest Ballerina Central packages when they are partially typed.
  • Improved sorting in the record type descriptor node context.
  • Introduced a code action to add local module dependencies to the Ballerina.toml file.
  • Introduced a code action to change the type of a variable in a let expression.
  • Introduced a code action to create a function for the expression of a select clause.
  • Improved completions in the service declaration node context.
  • Improved the language server simulator.

Bug fixes

To view bug fixes, see the GitHub milestone for Swan Lake Update 8 (2201.8.0) of the repositories below.

Ballerina packages updates

New features

Introduced the support for incorporating custom user repositories into the package management system in addition to the Ballerina Central repository.

This feature allows you to configure multiple repositories within the <USER_HOME>/.ballerina/Settings.toml file to publish your packages to your preferred repositories and retrieve packages from these repositories. You can seamlessly utilize these packages during the package-building process by explicitly defining dependencies in the Ballerina.toml file.

For more information on the custom package repositories support, see Manage dependencies.

Backward-incompatible changes

  • The switch to Java 17 may have an impact on Ballerina interoperability usage if there are incompatible changes. For example, Java 17 has some restrictions on using Java reflection with internal Java packages. For more information, see Java 17 support.

  • A type-checking bug that resulted in incorrect subtype relationships between records with optional fields and open records has been fixed.

    import ballerina/io;
    type Person record {
        string name;
    type Employee record {
        string name;
        int id?;
    public function main() {
        Person person = {name: "May"};
        Employee employee = person; // Compilation error now.
        io:println(person is Employee); // Prints `false` now.
  • Updated the analysis of the init method of an isolated object to disallow invalid transferring in/out of values that violated the isolated root invariant.

    type Node record {|
        readonly string path;
        map<string[]>? app = ();
    isolated class Class {
        private Node node;
        private Node[] arr = [];
        function init(Node node) {
            self.node = node.clone();
            self.arr.push(node); // Compilation error now.
            self.arr[0] = node; // Compilation error now.
  • Disallowed mutable objects in annotations.

    type Validator object {
        function validate(anydata data) returns error?;
    type AnnotationData record {|
        string name;
        Validator validator;
    annotation AnnotationData config on type; // Compilation error now.
  • Disallowed using field access with a map of xml. This was previously allowed incorrectly.

    map<xml> m = {a: xml `foo`};
    xml x = check m.a; // Compilation error now.
  • A bug that permitted uninitialized variables to evade detection when utilizing the on fail clause has been fixed.

    public function main() {
        int resultInt;
        transaction {
            resultInt = check calculateDefaultValue(true);
            check commit;
        } on fail {
            io:println("Failed to initialize resultInt");
        resultInt += 1; // Compilation error now.
  • A bug that resulted in incorrect type inference within query expressions when there is no expected type has been addressed. Previously, when iterating over a map without explicitly specifying an expected type, the resulting type of the query expression was erroneously inferred as an array. This misinterpretation has now been rectified and is properly restricted.

    function filterEmployeesByDepartment(map<Employee> employees, string department) {
        var result = from var e in employees // Compilation error now.
            where e.department == department
            select e.name;
  • A bug that allowed ignoring possible completion with an error when using the collect clause in a query expression has been fixed.

    function calculateTotalSalary(stream<Employee, error?> strm, string dept) {
        int total = from var {department, salary} in strm // Compilation error now.
            where department == dept
            collect sum(salary);
  • A bug related to deciding the types of numeric literals has been fixed.

    2f|1 a = 2; // Compilation error now, `2` is considered to be `int`.
    3d|6 b = 3; // Compilation error now, `3` is considered to be `int`.
    3d|4f|6 b = 4; // Compilation error now, `4` is considered to be `int`.
  • A bug that allowed an anydata value to be used in contexts expecting an anydata & readonly value has been fixed.

    public function main() {
        anydata a = [];
        anydata & readonly b = a; // Compilation error now.
  • A bug that allowed using object type inclusion with a readonly service object in a readonly non-service class has been fixed.

    public type A readonly & service object {
        isolated remote function execute() returns int;
    readonly client class B {
        *A; // Compilation error now.
        isolated remote function execute() returns int {
            return 2;
  • A bug that caused the runtime error messages to include the flattened representation of a union type instead of the name used in the type definition has been fixed.

    type AC map<int>|string;
    public function main() returns error? {
        map<anydata> x = {a: "Ballerina"};
        AC|boolean _ = check x.cloneWithType();

    This now fails with "'map<anydata>' value cannot be converted to '(AC|boolean)'" instead of "'map<anydata>' value cannot be converted to '(map<int>|string|boolean)'".

  • A bug that resulted in an incorrect value being used as the default value of a class field, when the default value refers to a module-level variable that is also used in the default value of a function parameter has been fixed.

    import ballerina/io;
    int defaultTemperature = 25;
    public class TemperatureSensor {
        public string location;
        public int temperature = defaultTemperature;
        public function init(string location) {
            self.location = location;
        public function setDefaultTemperature(int temp) {
            self.temperature = temp;
    public function getTemperature(string location, int temperature = defaultTemperature) returns int {
        return temperature;
    public function main() {
        TemperatureSensor livingRoomSensor = new ("Living Room");
        io:println("Current temperature in the " + livingRoomSensor.location + ": " + livingRoomSensor.temperature.toString() + "°C");
        // Prints `Current temperature in the Living Room: 25°C` now.
        int defaultTemp = getTemperature("Kitchen");
        io:println("Default temperature in the Kitchen: " + defaultTemp.toString() + "°C");
        // Prints `Default temperature in the Kitchen: 25°C` now.
  • Modified the behavior of the runtime Java APIs to support the intersection type.

  • Modified the behavior of the Semantic API typeDescriptor() methods to return the intersection type symbol instead of the effective type symbol (i.e., the symbol of the corresponding non-intersection type that is computed to represent the same value space).

    // `TypeSymbol` of `A` will now be an `IntersectionTypeSymbol` instead of `ArrayTypeSymbol`.
    type A int[] & readonly;
  • Removed support for the AES/GCM/PKCS5Padding encryption algorithm in the crypto package due to its incompatibility with Java 17.