/*
* 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 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 used to assist in the creation of immutable classes.
* <p>
* It allows you to write classes in this shortened form:
* <pre class="groovyTestCase">
* {@code @groovy.transform.Immutable} class Customer {
* String first, last
* int age
* Date since
* Collection favItems
* }
* def d = new Date()
* def c1 = new Customer(first:'Tom', last:'Jones', age:21, since:d, favItems:['Books', 'Games'])
* def c2 = new Customer('Tom', 'Jones', 21, d, ['Books', 'Games'])
* assert c1 == c2
* </pre>
* The {@code @Immutable} annotation instructs the compiler to execute an
* AST transformation which adds the necessary getters, constructors,
* equals, hashCode and other helper methods that are typically written
* when creating immutable classes with the defined properties.
* <p>
* A class created in this way has the following characteristics:
* <ul>
* <li>The class is automatically made final.
* <li>Properties must be of an immutable type or a type with a strategy for handling non-immutable
* characteristics. Specifically, the type must be one of the primitive or wrapper types, Strings, enums,
* other {@code @Immutable} classes or known immutables (e.g. java.awt.Color, java.net.URI, java.util.UUID).
* Also handled are Cloneable classes, collections, maps and arrays, other "effectively immutable"
* classes with special handling (e.g. java.util.Date), and usages of java.util.Optional where the
* contained type is immutable (e.g. Optional<String>).
* <li>Properties automatically have private, final backing fields with getters.
* Attempts to update the property will result in a {@code ReadOnlyPropertyException}.
* <li>A map-based constructor is provided which allows you to set properties by name.
* <li>A tuple-style constructor is provided which allows you to set properties in the same order as they are defined.
* <li>Default {@code equals}, {@code hashCode} and {@code toString} methods are provided based on the property values.
* Though not normally required, you may write your own implementations of these methods. For {@code equals} and {@code hashCode},
* if you do write your own method, it is up to you to obey the general contract for {@code equals} methods and supply
* a corresponding matching {@code hashCode} method.
* If you do provide one of these methods explicitly, the default implementation will be made available in a private
* "underscore" variant which you can call. E.g., you could provide a (not very elegant) multi-line formatted
* {@code toString} method for {@code Customer} above as follows:
* <pre>
* String toString() {
* _toString().replaceAll(/\(/, '(\n\t').replaceAll(/\)/, '\n)').replaceAll(/, /, '\n\t')
* }
* </pre>
* If an "underscore" version of the respective method already exists, then no default implementation is provided.
* <li>{@code Date}s, {@code Cloneable}s and arrays are defensively copied on the way in (constructor) and out (getters).
* Arrays and {@code Cloneable} objects use the {@code clone} method. For your own classes,
* it is up to you to define this method and use deep cloning if appropriate.
* <li>{@code Collection}s and {@code Map}s are wrapped by immutable wrapper classes (but not deeply cloned!).
* Attempts to update them will result in an {@code UnsupportedOperationException}.
* <li>Fields that are enums or other {@code @Immutable} classes are allowed but for an
* otherwise possible mutable property type, an error is thrown.
* <li>You don't have to follow Groovy's normal property conventions, e.g. you can create an explicit private field and
* then you can write explicit get and set methods. Such an approach, isn't currently prohibited (to give you some
* wiggle room to get around these conventions) but any fields created in this way are deemed not to be part of the
* significant state of the object and aren't factored into the {@code equals} or {@code hashCode} methods.
* Similarly, you may use static properties (though usually this is discouraged) and these too will be ignored
* as far as significant state is concerned. If you do break standard conventions, you do so at your own risk and
* your objects may no longer be immutable. It is up to you to ensure that your objects remain immutable at least
* to the extent expected in other parts of your program!
* </ul>
* Immutable classes are particularly useful for functional and concurrent styles of programming
* and for use as key values within maps. If you want similar functionality to what this annotation
* provides but don't need immutability then consider using {@code @Canonical}.
* <p>
* Customising behaviour:
* <p>
* You can customise the toString() method provided for you by {@code @Immutable}
* by also adding the {@code @ToString} annotation to your class definition.
* <p>
* Limitations:
* <ul>
* <li>
* As outlined above, Arrays and {@code Cloneable} objects use the {@code clone} method. For your own classes,
* it is up to you to define this method and use deep cloning if appropriate.
* </li>
* <li>
* As outlined above, {@code Collection}s and {@code Map}s are wrapped by immutable wrapper classes (but not deeply cloned!).
* </li>
* <li>
* Currently {@code BigInteger} and {@code BigDecimal} are deemed immutable but see:
* http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6348370
* </li>
* <li>
* {@code java.awt.Color} is treated as "effectively immutable" but is not final so while not normally used with child
* classes, it isn't strictly immutable. Use at your own risk.
* </li>
* <li>
* {@code java.util.Date} is treated as "effectively immutable" but is not final so it isn't strictly immutable.
* Use at your own risk.
* </li>
* <li>
* Groovy's normal map-style naming conventions will not be available if the first property
* has type {@code LinkedHashMap} or if there is a single Map, AbstractMap or HashMap property.
* </li>
* </ul>
* <p>More examples:</p>
--------------------------------------------------------------------------------
* <pre class="groovyTestCase">
* import groovy.transform.*
*
* @Canonical
* class Building {
* String name
* int floors
* boolean officeSpace
* }
*
* // Constructors are added.
* def officeSpace = new Building('Initech office', 1, true)
*
* // toString() added.
* assert officeSpace.toString() == 'Building(Initech office, 1, true)'
*
* // Default values are used if constructor
* // arguments are not assigned.
* def theOffice = new Building('Wernham Hogg Paper Company')
* assert theOffice.floors == 0
* theOffice.officeSpace = true
*
* def anotherOfficeSpace = new Building(name: 'Initech office', floors: 1, officeSpace: true)
*
* // equals() method is added.
* assert anotherOfficeSpace == officeSpace
*
* // equals() and hashCode() are added, so duplicate is not in Set.
* def offices = [officeSpace, anotherOfficeSpace, theOffice] as Set
* assert offices.size() == 2
* assert offices.name.join(',') == 'Initech office,Wernham Hogg Paper Company'
*
* @Canonical
* @ToString(excludes='age') // Customize one of the transformations.
* class Person {
* String name
* int age
* }
*
* def mrhaki = new Person('mrhaki', 37)
* assert mrhaki.toString() == 'Person(mrhaki)'
* </pre>
*
* @author Paul King
* @author Andre Steingress
* @see groovy.transform.ToString
* @see groovy.transform.Canonical
* @since 1.7
*/
@java.lang.annotation.Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.ImmutableASTTransformation")
public @interface Immutable {
/**
* Allows you to provide {@code @Immutable} with a list of classes which
* are deemed immutable. By supplying a class in this list, you are vouching
* for its immutability and {@code @Immutable} will do no further checks.
* Example:
* <pre>
* import groovy.transform.*
* {@code @Immutable}(knownImmutableClasses = [Address])
* class Person {
* String first, last
* Address address
* }
*
* {@code @TupleConstructor}
* class Address {
* final String street
* }
* </pre>
*
* @since 1.8.7
*/
Class[] knownImmutableClasses() default {};
/**
* Allows you to provide {@code @Immutable} with a list of property names which
* are deemed immutable. By supplying a property's name in this list, you are vouching
* for its immutability and {@code @Immutable} will do no further checks.
* Example:
* <pre>
* {@code @groovy.transform.Immutable}(knownImmutables = ['address'])
* class Person {
* String first, last
* Address address
* }
* ...
* </pre>
*
* @since 2.1.0
*/
String[] knownImmutables() default {};
/**
* If {@code true}, this adds a method {@code copyWith} which takes a Map of
* new property values and returns a new instance of the Immutable class with
* these values set.
* Example:
* <pre class="groovyTestCase">
* {@code @groovy.transform.Immutable}(copyWith = true)
* class Person {
* String first, last
* }
*
* def tim = new Person( 'tim', 'yates' )
* def alice = tim.copyWith( first:'alice' )
*
* assert tim.first == 'tim'
* assert alice.first == 'alice'
* </pre>
* Unknown keys in the map are ignored, and if the values would not change
* the object, then the original object is returned.
*
* If a method called {@code copyWith} that takes a single parameter already
* exists in the class, then this setting is ignored, and no method is generated.
*
* @since 2.2.0
*/
boolean copyWith() default false;
}