groovy.transform.InheritConstructors Maven / Gradle / Ivy

/*
 * Copyright 2008-2013 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.transform;

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;

/**
 * Class annotation to make constructors from a super class available in a sub class.
 * 
 * {@code @InheritConstructors} saves you typing some boilerplate code.
 * 

 * Example usage:
 * 
 * class Person {
 *     String first, last
 *     Person(String first, String last) {
 *         this.first = first
 *         this.last = last.toUpperCase()
 *     }
 * }
 *
 * {@code @InheritConstructors}
 * class PersonAge extends Person {
 *     int age
 * }
 *
 * def js = new PersonAge('John', 'Smith')
 * js.age = 25
 * println "$js.last, $js.first is $js.age years old"
 * // => SMITH, John is 25 years old
 * 
 * for this case, the PersonAge class will be
 * equivalent to the following code:
 *  * class PersonAge extends Person {
 *     PersonAge(String first, String last) {
 *         super(first, last)
 *     }
 *     int age
 * }
 * 
 * You may add additional constructors in addition to inherited ones.
 * If the argument types of a supplied constructor exactly match those
 * of a parent constructor, then that constructor won't be inherited.
 * 
 * Style note: Don't go overboard using this annotation.
 * Typical Groovy style is to use named-arg constructors when possible.
 * This is easy to do for Groovy objects or any objects following JavaBean
 * conventions. In other cases, inheriting the constructors may be useful.
 * However, sub-classes often introduce new properties and these are often best
 * set in a constructor; especially if that matches the style adopted
 * in parent classes. So, even for the example above, it may have been
 * better style to define an explicit constructor for PersonAge
 * that also set the age property. Sometimes, consistent
 * style is much more important than saving a few keystrokes.
 * 

 * As another example, this:
 * 
 * {@code @InheritConstructors} class CustomException extends RuntimeException { }
 * 
 * is equivalent to this:
 *  * class CustomException extends RuntimeException {
 *     CustomException() {
 *         super()
 *     }
 *     CustomException(String message) {
 *         super(message)
 *     }
 *     CustomException(String message, Throwable cause) {
 *         super(message, cause)
 *     }
 *     CustomException(Throwable cause) {
 *         super(cause)
 *     }
 * }
 * 
 *
 * Advanced note:If you create Groovy constructors with optional
 * arguments this leads to multiple constructors created in the byte code.
 * The expansion to multiple constructors occurs in a later phase to
 * this AST transformation. This means that you can't override (i.e. not
 * inherit) the constructors with signatures that Groovy adds later.
 * If you get it wrong you will get a compile-time error about the duplication.
 *
 * @author Paul King
 * @since 1.7.3
 */
@java.lang.annotation.Documented
@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.TYPE})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.InheritConstructorsASTTransformation")
public @interface InheritConstructors {
}