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Groovy example source code file (Newify.java)

This example Groovy source code file (Newify.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Groovy tags/keywords

annotation, class, class, groovyasttransformationclass, groovyasttransformationclass, newify, newify, target, target

The Groovy Newify.java source code

/*
 * Copyright 2008-2011 the original author or authors.
 *
 * Licensed 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.lang;

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;

/**
 * Annotation that supports writing constructor call expressions without the 'new'
 * keyword. Instead they can be written "Ruby-style" as a method call to a 'new'
 * method or "Python-style" by just omitting the keyword missing.
 * </p>
 * It allows you to write code snippets like this ("Python-style"):
 * <pre>
 * {@code @Newify([Tree,Leaf])} class MyTreeProcessor {
 *     def myTree = Tree(Tree(Leaf("A"), Leaf("B")), Leaf("C"))
 *     def process() { ... }
 * }
 * </pre>
 * or this ("Ruby-style"):
 * <pre>
 * {@code @Newify} class MyTreeProcessor {
 *     def myTree = Tree.new(Tree.new(Leaf.new("A"), Leaf.new("B")), Leaf.new("C"))
 *     def process() { ... }
 * }
 * </pre>
 *
 * After the AST transformation, the following code is passed on for further compilation:
 * <pre>
 * class MyTreeProcessor {
 *     def myTree = new Tree(new Tree(new Leaf("A"), new Leaf("B")), new Leaf("C"))
 *     def process() { ... }
 * }
 * </pre>
 * The annotation can be used on a whole class as shown above or selectively on a particular
 * method, constructor or field.
 *
 * The "Ruby-style" new conversions occur automatically unless the 'auto=false'
 * flag is given when using the annotation. You might do this if you create a new method
 * using meta programming.
 *
 * The "Python-style" conversions require you to specify each class on which you want them
 * to apply. The transformation then works by matching the basename of the provided classes to any
 * similarly named instance method calls not specifically bound to an object, i.e. associated
 * with the 'this' object. In other words <code>Leaf("A") would be transformed to
 * <code>new Leaf("A") but x.Leaf("A") would not be touched.
 *
 * An example showing how to use the annotation at different levels:
 * <pre>
 * {@code @Newify(auto=false, value=Foo)}
 * class Main {
 *     {@code @Newify} // turn auto on for field
 *     def field1 = java.math.BigInteger.new(42)
 *     def field2, field3, field4
 *
 *     {@code @Newify(Bar)}
 *     def process() {
 *         field2 = Bar("my bar")
 *     }
 *
 *     {@code @Newify(Baz)}
 *     Main() {
 *         field3 = Foo("my foo")
 *         field4 = Baz("my baz")
 *     }
 * }
 * </pre>
 *
 * The annotation is intended to be used sparingly; perhaps in DSL scenarios or when
 * using deeply nested structural types. In particular, there is no support for using
 * the facility with two similarly named classes from different packages at the same time.
 * Though it is OK to have different packages in different contexts. Also, there is
 * no support for turning "Ruby-style" conversions off at the method, constructor or
 * field level if already turned on at the class level.
 *
 * @author Paul King
 */
@java.lang.annotation.Documented
@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.TYPE, ElementType.FIELD, ElementType.LOCAL_VARIABLE})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.NewifyASTTransformation")
public @interface Newify {
    Class[] value();

    /**
     * @return if automatic conversion of "Ruby-style" new method calls should occur
     */
    boolean auto() default true;
}

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