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Groovy: A powerful, dynamic language for the JVM
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/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing,
 *  software distributed under the License is distributed on an
 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
 *  under the License.
 */
package groovy.transform;

import groovy.lang.Script;
import org.codehaus.groovy.transform.GroovyASTTransformationClass;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Variable annotation used for changing the base script class of the current script.
 * 
 * The type of the variable annotated with {@code @BaseScript} must extend {@link 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
 * {@link org.codehaus.groovy.control.CompilerConfiguration} of {@link groovy.lang.GroovyShell}
 * Example usage:
 * 
 * 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()
 *         }
 *     }
 * }
 *
 * {@code @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'
 * 
 * 
 * @author Paul King
 * @author Vladimir Orany
 * @author Jim White
 * @since 2.2.0
 */
@java.lang.annotation.Documented
@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.LOCAL_VARIABLE, ElementType.PACKAGE, ElementType.TYPE /*, ElementType.IMPORT*/})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.BaseScriptASTTransformation")
public @interface BaseScript {
    Class value() default Script.class;
}