scala.annotation

meta

package meta

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.

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  1. final class beanGetter extends Annotation with StaticAnnotation

    Consult the documentation in package scala.annotation.meta.

  2. final class beanSetter extends Annotation with StaticAnnotation

    Consult the documentation in package scala.annotation.meta.

  3. final class companionClass extends Annotation with StaticAnnotation

    When defining an implicit class, the Scala compiler creates an implicit conversion method for it.

    When defining an implicit class, the Scala compiler creates an implicit conversion method for it. Annotations @companionClass and @companionMethod control where an annotation on the implicit class will go. By default, annotations on an implicit class end up only on the class.

  4. final class companionMethod extends Annotation with StaticAnnotation

    When defining an implicit class, the Scala compiler creates an implicit conversion method for it.

    When defining an implicit class, the Scala compiler creates an implicit conversion method for it. Annotations @companionClass and @companionMethod control where an annotation on the implicit class will go. By default, annotations on an implicit class end up only on the class.

  5. final class companionObject extends Annotation with StaticAnnotation

    Currently unused; intended as an annotation target for classes such as case classes that automatically generate a companion object

  6. final class field extends Annotation with StaticAnnotation

    Consult the documentation in package scala.annotation.meta.

  7. final class getter extends Annotation with StaticAnnotation

    Consult the documentation in package scala.annotation.meta.

  8. final class languageFeature extends Annotation with StaticAnnotation

    An annotation giving particulars for a language feature in object scala.language.

  9. final class param extends Annotation with StaticAnnotation

    Consult the documentation in package scala.annotation.meta.

  10. final class setter extends Annotation with StaticAnnotation

    Consult the documentation in package scala.annotation.meta.

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