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Groovy: A powerful, dynamic language for the JVM
There is a newer version: 3.0.21
/*
 * Copyright 2008 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.
 * 
 * It allows you to write code snippets like this ("Python-style"):
 *  * {@code @Newify([Tree,Leaf])} class MyTreeProcessor {
 *     def myTree = Tree(Tree(Leaf("A"), Leaf("B")), Leaf("C"))
 *     def process() { ... }
 * }
 * 
 * or this ("Ruby-style"):
 *  * {@code @Newify()} class MyTreeProcessor {
 *     def myTree = Tree.new(Tree.new(Leaf.new("A"), Leaf.new("B")), Leaf.new("C"))
 *     def process() { ... }
 * }
 * 
 *
 * After the AST transformation, the following code is passed on for further compilation:
 *  * class MyTreeProcessor {
 *     def myTree = new Tree(new Tree(new Leaf("A"), new Leaf("B")), new Leaf("C"))
 *     def process() { ... }
 * }
 * 
 * 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 Leaf("A") would be transformed to
 * new Leaf("A") but x.Leaf("A") would not be touched.
 *
 * An example showing how to use the annotation at different levels:
 *  * {@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")
 *     }
 * }
 * 
 *
 * 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
 */
@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.TYPE, ElementType.FIELD})
@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;
}