= Vert.x for Kotlin

If you are using Maven or Gradle, add the following dependency to the _dependencies_ section of your
project descriptor to access the Vert.x Core API and enable the Kotlin support:

* Maven (in your `pom.xml`):

[source,xml,subs="+attributes"]
----
<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-core</artifactId>
<version>4.2.2</version>
</dependency>
<dependency>
 <groupId>io.vertx</groupId>
 <artifactId>vertx-lang-kotlin</artifactId>
 <version>4.2.2</version>
</dependency>
----

* Gradle (in your `build.gradle` file):

[source,groovy,subs="+attributes"]
----
compile "io.vertx:vertx-core:4.2.2"
compile "io.vertx:vertx-lang-kotlin:4.2.2"
----

== Verticles

=== Writing Verticles

Writing a Verticle with Kotlin is achieved the same way you write a Java Verticle by
extending the `link:../../apidocs/io/vertx/core/AbstractVerticle.html[AbstractVerticle]`.

Here's an example verticle:

[source, kotlin]
----
import io.vertx.core.AbstractVerticle

class MyVerticle : AbstractVerticle() {

 // Called when verticle is deployed
 override fun start() {
 }

 // Optional - called when verticle is undeployed
 override fun stop() {
 }
}
----

Please refer to the Java documentation.

== Data Objects builders

Data Objects play an essential role in the Vert.x stack (a Data Object is a type that can be converted to/from JSON).

For example, Vert.x modules often use Data Objects for the configuration of servers:

[source,kotlin]
----
val classic: HttpServerOptions = HttpServerOptions()
 .setIdleTimeout(5)
 .setIdleTimeoutUnit(TimeUnit.MINUTES)
 .setLogActivity(true)
----

While the above construct is valid, there is a more idiomatic way of configuring Data Objects.
In Kotlin, all Data Objects have a builder method suffixed with `Of`:

[source,kotlin]
----
val options = httpServerOptionsOf(idleTimeout = 5, idleTimeoutUnit = TimeUnit.MINUTES, logActivity = true)
----

== JSON

Unlike some other languages, Java does not have first class support for http://json.org/[JSON] so we provide
two classes to make handling JSON in your Vert.x applications a bit easier.

Use the `link:../../apidocs/io/vertx/core/json/JsonObject.html[JsonObject]` class to represent JSON objects and the `link:../../apidocs/io/vertx/core/json/JsonArray.html[JsonArray]`
class to represent JSON arrays, you can refer to the Java documentation for more details.

=== Builders

Builders are provided to provide a more fluent JSON construction:

[source, kotlin]
----
// The json builder declares a JSON structure
val result = json {

 // in this structure the obj function can be used

 // takes a vararg of Kotlin pairs
 obj(
   "key_1" to 1,
   "key_2" to 2,
   "key_3" to 3
 )

 // or an iterable of Kotlin pairs
 obj((1..3).map { "key_$it" to it })

 // or a Map<String, Any?>
 obj(someMap)

 // apply function on object receiver
 obj {
   for (i in 1..3) {
     put("key_$i", i)
   }
 }
}
----

You can also build JSON arrays:

[source, kotlin]
----
// The json builder declares a JSON structure
val result = json {

 // in this structure the array function can be used

 // takes a vararg of values
 array("1", "2", "3")

 // or an iterable of values
 array((1..3).map { "$it" })

 // apply function on array receiver
 array {
   for (i in 1..3) {
     add("$i")
   }
 }
}
----

Of course it is possible to mix objects and arrays

[source, kotlin]
----
// The json builder declares a JSON structure
val result = json {

 "firstName" to "Dale",
 "lastName" to "Cooper",
 "age" to 64,
 "names" to array("Dale", "Bartholomew")
}
----

=== Postscript operator overloading

The Kotlin postscript operator is overloaded for JSON object and array:

[source, kotlin]
----
print(someObject["firstName"]);
print(someArray[4]);
----