Swan Lake Beta6

Overview of Ballerina Swan Lake Beta6

This is the sixth Beta release in a series of planned Alpha and Beta releases leading up to the Ballerina Swan Lake GA release.

It introduces the new language features planned for the Swan Lake GA release and includes improvements and bug fixes done to the compiler, runtime, standard library, and developer tooling after the Swan Lake Beta5 release.

Updating Ballerina

If you are already using Ballerina, you can use the update tool to directly update to Ballerina Swan Lake Beta6 as follows.

To do this, first, execute the command below to get the update tool updated to its latest version.

bal update

If you are using an update tool version below 0.8.14, execute the ballerina update command to update it. Next, execute the command below to update to Swan Lake Beta5.

bal dist pull slbeta6

Installing Ballerina

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

Language updates


Updated the static type of the unary plus expression to be the same as the static type of the operand. The assignments below are allowed now.

public function main() {
    int:Unsigned8 a = 32;
    int:Unsigned8 b = +a;

    int:Unsigned16 c = 43;
    int:Unsigned16 d = +c;

    int:Unsigned32 e = 54;
    int:Unsigned32 f = +e;

    byte g = 127;
    byte h = +g;

    int:Signed8 i = -32;
    int:Signed8 j = +i;

    int:Signed16 k = -65;
    int:Signed16 l = +k;

    int:Signed32 m = -64;
    int:Signed32 n = +m;

Bug fixes

To view bug fixes, see the GitHub milestone for Swan Lake Beta6.

Standard library updates

New features

graphql package

Added support for the GraphQL list type inputs.

http package

Introduced request and request error interceptors at the service level.

xmldata package

Added support to convert an XML to a record.

time package

Added time zone handling support.


http package

Allowed listener-level interceptors to have only the default path.

Breaking changes

graphql package

Deprecated the add function in the graphql:Context object and introduced the set function.

Old method:

graphql:Context context = new;
graphql:Error? result = context.add("key", "<value>"); // Can return an error

New method:

graphql:Context context = new;
context.set("key", "<value>"); // Does not return anything

http package

  • Changed the RequestContext:add function to RequestContext:set.

    service class DefaultRequestInterceptor {
        resource function 'default [string... path](http:RequestContext ctx) returns http:NextService|error? {
            ctx.set("last-interceptor", "default-interceptor");
            return ctx.next();
  • Changed the parseHeader() function to support multiple header values.

    http:HeaderValue[] values = check http:parseHeader("text/plain;level=1;q=0.6, application/xml;level=2");

Bug fixes

To view bug fixes, see the GitHub milestone for Swan Lake Beta6.

Developer tools updates


OpenAPI tool

  • Added the --with-tests option for the OpenAPI client generation command, which will generate a test file template for all the relevant remote functions of the client. For example,

    bal openapi -i <openapi contract> --mode client --with-tests

  • Added the --export-openapi option for the build command, which will generate OpenAPI contract files for all the services in the current package. For example,

    bal build --export-openapi


  • Introduced the --target-dir flag to the run, test, doc, and clean commands. With this, you can pass a custom directory to the aforementioned commands.
  • Added support for creating packages using template packages in Ballerina Central. For example, bal new -t wso2/choreo_sample.

Breaking changes

Test framework

Improved the assertFail function to eliminate the fake return/panic that had to be added after the statement. The signature of the function is changed as follows.

Old signature:

public isolated function assertFail(string msg = "Test Failed!");

New signature:

public isolated function assertFail(string msg = "Test Failed!") returns never;

For example, the function below, which compiled without an issue in Beta5 will throw an unreachable code compilation error after this signature change.

function testFunc(int|string val) returns int? {
  if (val is int) {
      return val;
  } else {
  return; //Remove this fake return statement to compile with Swan lake Beta6.

Bug fixes

To view bug fixes, see the GitHub milestone for Swan Lake Beta3 of the repositories below.

Ballerina packages updates

New features

Added support to add an icon field under the [package] table. For example,

org = "ballerinax"
name = "googleapis.gmail"
version = "0.1.0”
icon = “images/icon.png”

Info: The specified icon file will be packaged into the docs/ directory of the Ballerina archive (.bala). Only the .png format is supported for the icon.