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Overview of Ballerina 0.980

Kishanthan Thangarajah
26 July 2018

Ballerina 0.980.0 release included some type system improvements and new features. This release also focused on stabilizing the platform with lot of bug fixes and improvements.

Object syntax change

Object type descriptor syntax now supports visibility modifiers for both object fields and functions. There are three types of access modifiers (public, private, no-modifier) as explained below.

ublic type Person object {
   // public - visible everywhere
   public string name;

   // private - visible only within object and its member functions
   private int age;

   // no-modifier - visible only within same package
   string email;

Closed and open records

An open record can contain extra fields, that is, fields other than those named by individual type descriptors in the record type definition. By default, records can contain extra fields with any value without any changes to record definition as explained below.

ype Person record {
   string name,
   int age = 10,

/ The "country" is an extra field, which is not defined in the person
/ type descriptor.
erson tom = { name : "tom", age : 20, country : "USA"};

/ You can access the "country" field similar to other fields, but the
/ return type will be `any`.
ny country =;

Additional fields can be defined by using an optional RecordRestType... at the end of the record definition. In the above example, the Person record definition is equivalent to the definition with any....

ype Person record {
   string name,
   int age = 10,

The “rest fields” can also be constrained to other types. Below example shows how it is constrained to string type.

ype Person record {
   string name,
   int age = 10,


erson tom = { name : "tom", age : 20, country : "USA"};
tring country =;

A closed record cannot contain any extra fields other than what is defined. A closed record can be defined with RecordRestType being ! as below.

ype Person record {
   string name,
   int age = 10,

/ Following will result in a compile time error.
erson tom = { name : "tom", age : 20, country : "USA"};

Fixed length arrays

The length of an array can be fixed by providing the array length with the array type descriptor.

nt[5] array1 = [2, 15, 200, 1500, 5000];

/ Following creates an integer array of size five, filled with
/ default integer values
nt[5] array2;

An array length of !... means that the length of the array is to be implied from the context; as shown below:

/ Following creates a sealed integer array of size 3.
nt[!...] sealedArray = [1, 3, 5];

Byte type

The byte type represents the set of 8-bit unsigned integers. The implicit initial value of the byte type is 0. Value space for byte is 0-255 both inclusive.

The following is an example of byte definition.

yte c = 23;

Along with general byte array type, there is also a special syntax for defining base64 and base16 based array of bytes. With this, blob type is removed and replaced by byte array.

yte[] arr1 = [5, 24, 56, 243];
yte[] arr2 = base16 `aeeecdefabcd12345567888822`;
yte[] arr3 = base64 `aGVsbG8gYmFsbGVyaW5hICEhIQ==`;

Bitwise AND (&), OR (|), XOR (^)

Bitwise operations AND (&), OR (|), XOR (^) have been added for byte type and int type with the following rules.

Both the right-hand-side and left-hand-side of the expression should be of the same type (byte or int), and the expected type will be also of the same type. If this is not the case, it will result in a compilation error. An explicit conversion operation should be applied if the type of one side is not the same as the other side.

yte a = 13;
yte b = 45;
yte c = a & b;
yte d = a | b;
yte e = a ^ b;

Table expression

A table is intended to be similar to a relational database table. A table value contains an immutable set of column names and a set of data rows. Syntax for defining a table and adding data rows is as below.

able<Person> t1 = table {
{ primarykey id, primarykey salary, name, age, married }, [
	 {1, 300.5, "jane",  30, true},
	 {2, 302.5, "anne",  23, false},
	 {3, 320.5, "john",  33, true}

/ We can also create the row records seperately and then use it with
/ table definition
erson p1 = { id: 1, age: 30, salary: 300.50, name: "jane", married: true };
erson p2 = { id: 1, age: 30, salary: 300.50, name: "jane", married: true };

able<Person> t1 = table {
{ primarykey id, salary, name, age, married },
[p1, p2]

Map access

Values of a map can be accessed using index-based syntax as well as field-access syntax. Accessing a value using field-based syntax returns the value if the key exists. Otherwise a runtime error is thrown. Index-based syntax also will return the value if the key exists. However, it will return a null value if the key does not exist. This would also mean that, for a constrained map, the type of the return value for the index-based syntax is always the constraint_type|() as explained below.

ap<string> m = {"fname" : "John", "lname" : "Doe"}

/ Field based access
tring firstName = m.fname;

/ Following will result in a runtime error
tring middleName = m.mname;

/ Index based access
tring? firstName = m["fname"];

/ Following will return null
tring? middleName = m["mname"];

Ballerina observability

  • New API's have been introduced with ballerina observability functionality, such that developers can define their own trace blocks and metrics as explained below.
  • Developers can attach the trace information of their code block to the default Ballerina traces, or a new trace as below.
/ Create and attach span to the default Ballerina request trace.
nt spanId = check observe:startSpan("Child Span");
   // Do Something
 = observe:finishSpan(spanId);

/ Create a completely new trace.
nt spanId = observe:startRootSpan("Parent Span");
   //Do Something
nt spanId2 = check observe:startSpan("Child Span", parentSpanId = spanId);
   // Do Something
 = observe:finishSpan(spanId2);
   // Do Something
 = observe:finishSpan(spanId);
  • Developers can create a metric (counter or gauge) and have have their own measurements. The created metric can be registered in order to include its measurements to reporters such as Prometheus as below.
/ Create counter and register.
ap<string> counterTags = { "method": "GET" };
bserve:Counter counterWithTags = new ("CounterWithTags",
   desc = "Some description", tags = counterTags);
ounterWithTags.register() but {
  error e => log:printError("Cannot register the counter", err = e)

/ Create statistics config to enable statistics calculation.
bserve:StatisticConfig[] statsConfigs = [];
bserve:StatisticConfig config =
   {timeWindow:30000, percentiles:[0.33, 0.5, 0.9, 0.99], buckets:3};

/ Create gauge and register.
bserve:Gauge gaugeWithStats = new ("GaugeWithTags",
   desc = "Some description", tags = gaugeTags,
   statisticConfig = statsConfigs);
  • All metrics registered can be retrieved and looked up individually as below.
/ Get All Metrics
bserve:Metric[] metrics = observe:getAllMetrics();
oreach metric in metrics {
   // Do something.

/ Look up a registered metric.
ap<string> tags = { "method": "GET" };
bserve:Counter|observe:Gauge|() metric =
   observe:lookupMetric("MetricName", tags = tags);
atch metric {
   observe:Counter counter => {
   observe:Gauge gauge => {
           gauge.increment(amount = 10.0);
   () => {
          io:println("No Metric Found!");

Standard library improvements

  • With the inclusion of byte[], WebSocket related signatures of resources such as onBinary, onPing, and onPong and functions such as pushBinary(), ping(), and pong() now have byte[] in their signature instead of a blob.
  • The HTTP transport error handler has been improved so that it recovers execution from inbound/outbound failures such as idle socket timeout and abrupt connection closure.
  • The circuit breaker now supports request volume threshold parameter. This parameter sets the minimum number of requests in a RollingWindow that will trip the circuit. So the rollingWindow configurations can be specified as below.
ollingWindow : {
     timeWindowMillis: 10000,
     bucketSizeMillis: 2000,
     requestVolumeThreshold: 10

Build and package management

  • The Ballerina build command output has been enhanced with more details about the build. Also by default, the test module will now be executed with the build command.
  • Ballerina push command now mandates the Ballerina build also along with it, which make sure that packages are built before it is pushed to the Central.
  • Ballerina Central now supports to view previous versions of a package. It also now shows Ballerina version compatibility section.

IDEs and language server

  • Composer is now shipped as a native Electron App.
  • Language server now includes source code formatting and also supports finding all symbols in a document and in the workspace.
  • IntelliJ IDEA Ballerina Plugin has added improvements for the Ballerina source code debugger.