Variable annotation used for changing the base script class of the current script.

The type of the variable annotated with @BaseScript must extend groovy.lang.Script. It will be used as the base script class. The annotated variable will become shortcut to this object. Using this annotation will override base script set by Groovy compiler or org.codehaus.groovy.control.CompilerConfiguration of groovy.lang.GroovyShell Example usage:

abstract class CustomScript extends Script {
    int getTheMeaningOfLife() { 42 }
}

@BaseScript CustomScript baseScript

assert baseScript == this
assert theMeaningOfLife == 42
assert theMeaningOfLife == baseScript.theMeaningOfLife

In this example, the base script of the current script will be changed to CustomScript allowing usage of getTheMeaningOfLife() method. baseScript variable will become typed shortcut for this object which enables better IDE support.

The custom base script may implement the run() method and specify a different method name to be used for the script body by declaring a single abstract method. For example:

abstract class CustomScriptBodyMethod extends Script {
    abstract def runScript()
    def preRun() { println "preRunning" }
    def postRun() { println "postRunning" }
    def run() {
        preRun()
        try {
            3.times { runScript() }
        } finally {
            postRun()
        }
    }
}

@BaseScript CustomScriptBodyMethod baseScript
println "Script body run"

That will produce the following output:

preRunning
Script body run
Script body run
Script body run
postRunning

Note that while you can declare arguments for the script body's method, as the AST is currently implemented they are not accessible in the script body code.

More examples:

// Simple Car class to save state and distance.
class Car {
    String state
    Long distance = 0
}

// Custom Script with methods that change the Car's state.
// The Car object is passed via the binding.
abstract class CarScript extends Script {
    def start() {
        this.binding.car.state = 'started'
    }

    def stop() {
        this.binding.car.state = 'stopped'
    }

    def drive(distance) {
        this.binding.car.distance += distance
    }
}


// Define Car object here, so we can use it in assertions later on.
def car = new Car()
// Add to script binding (CarScript references this.binding.car).
def binding = new Binding(car: car)

// Configure the GroovyShell.
def shell = new GroovyShell(this.class.classLoader, binding)

// Simple DSL to start, drive and stop the car.
// The methods are defined in the CarScript class.
def carDsl = '''
start()
drive 20
stop()
'''


// Run DSL script.
shell.evaluate """
// Use BaseScript annotation to set script
// for evaluating the DSL.
@groovy.transform.BaseScript CarScript carScript

$carDsl
"""

// Checks to see that Car object has changed.
assert car.distance == 20
assert car.state == 'stopped'