scala.annotation.meta.package.scala Maven / Gradle / Ivy
The newest version!
/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala.annotation
/**
* When defining a field, the Scala compiler creates up to four accessors
* for it: a getter, a setter, and if the field is annotated with
* `@BeanProperty`, a bean getter and a bean setter.
*
* For instance in the following class definition
*
* {{{
* class C(@myAnnot @BeanProperty var c: Int)
* }}}
*
* there are six entities which can carry the annotation `@myAnnot`: the
* constructor parameter, the generated field and the four accessors.
*
* By default, annotations on (`val`-, `var`- or plain) constructor parameters
* end up on the parameter, not on any other entity. Annotations on fields
* by default only end up on the field.
*
* The meta-annotations in package `scala.annotation.meta` are used
* to control where annotations on fields and class parameters are copied.
* This is done by annotating either the annotation type or the annotation
* class with one or several of the meta-annotations in this package.
*
* ==Annotating the annotation type==
*
* The target meta-annotations can be put on the annotation type when
* instantiating the annotation. In the following example, the annotation
* `@Id` will be added only to the bean getter `getX`.
*
* {{{
* import javax.persistence.Id
* class A {
* @(Id @beanGetter) @BeanProperty val x = 0
* }
* }}}
*
* In order to annotate the field as well, the meta-annotation `@field`
* would need to be added.
*
* The syntax can be improved using a type alias:
*
* {{{
* object ScalaJPA {
* type Id = javax.persistence.Id @beanGetter
* }
* import ScalaJPA.Id
* class A {
* @Id @BeanProperty val x = 0
* }
* }}}
*
* ==Annotating the annotation class==
*
* For annotations defined in Scala, a default target can be specified
* in the annotation class itself, for example
*
* {{{
* @getter
* class myAnnotation extends Annotation
* }}}
*
* This only changes the default target for the annotation `myAnnotation`.
* When instantiating the annotation, the target can still be specified
* as described in the last section.
*/
package object meta