scala.reflect.api

# Constants

#### trait Constants extends AnyRef

EXPERIMENTAL

According to the section 6.24 "Constant Expressions" of the Scala language specification, certain expressions (dubbed constant expressions) can be evaluated by the Scala compiler at compile-time.

scala.reflect.api.Constants#Constant instances represent certain kinds of these expressions (with values stored in the `value` field and its strongly-typed views named `booleanValue`, `intValue` etc.), namely:

1. Literals of primitive value classes (bytes, shorts, ints, longs, floats, doubles, chars, booleans and voids).
2. String literals.
3. References to classes (typically constructed with scala.Predef#classOf).
4. References to enumeration values.

Such constants are used to represent literals in abstract syntax trees (the scala.reflect.api.Trees#Literal node) and literal arguments for Java class file annotations (the scala.reflect.api.Annotations#LiteralArgument class).

##### Example

The `value` field deserves some explanation. Primitive and string values are represented as themselves, whereas references to classes and enums are a bit roundabout.

Class references are represented as instances of scala.reflect.api.Types#Type (because when the Scala compiler processes a class reference, the underlying runtime class might not yet have been compiled). To convert such a reference to a runtime class, one should use the `runtimeClass` method of a mirror such as scala.reflect.api.Mirrors#RuntimeMirror (the simplest way to get such a mirror is using scala.reflect.runtime.package#currentMirror).

Enumeration value references are represented as instances of scala.reflect.api.Symbols#Symbol, which on JVM point to methods that return underlying enum values. To inspect an underlying enumeration or to get runtime value of a reference to an enum, one should use a scala.reflect.api.Mirrors#RuntimeMirror (the simplest way to get such a mirror is again scala.reflect.runtime.package#currentMirror).

    enum JavaSimpleEnumeration { FOO, BAR }

    import java.lang.annotation.*;
    @Retention(RetentionPolicy.RUNTIME)
    @Target({ElementType.TYPE})
    public @interface JavaSimpleAnnotation {
      Class<?> classRef();
      JavaSimpleEnumeration enumRef();
    }

    @JavaSimpleAnnotation(
      classRef = JavaAnnottee.class,
      enumRef = JavaSimpleEnumeration.BAR
    )
    public class JavaAnnottee {}

    import scala.reflect.runtime.universe._
    import scala.reflect.runtime.{currentMirror => cm}

    object Test extends App {
      val jann = typeOf[JavaAnnottee].typeSymbol.annotations(0).javaArgs
      def jarg(name: String) = jann(newTermName(name)).asInstanceOf[LiteralArgument].value

      val classRef = jarg("classRef").typeValue
      println(showRaw(classRef))             // TypeRef(ThisType(), JavaAnnottee, List())
      println(cm.runtimeClass(classRef))     // class JavaAnnottee

      val enumRef = jarg("enumRef").symbolValue
      println(enumRef)                       // value BAR

      val siblings = enumRef.owner.info.decls
      val enumValues = siblings.filter(sym => sym.isVal && sym.isPublic)
      println(enumValues)                    // Scope{
                                             //   final val FOO: JavaSimpleEnumeration;
                                             //   final val BAR: JavaSimpleEnumeration
                                             // }

      // doesn't work because of https://issues.scala-lang.org/browse/SI-6459
      // val enumValue = mirror.reflectField(enumRef.asTerm).get
      val enumClass = cm.runtimeClass(enumRef.owner.asClass)
      val enumValue = enumClass.getDeclaredField(enumRef.name.toString).get(null)
      println(enumValue)                     // BAR
    }

Self Type
  Universe

Linear Supertypes
AnyRef, Any
Known Subclasses
JavaUniverse, Universe, Universe
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2. Alphabetic
3. By inheritance

Inherited

1. Constants
2. AnyRef
3. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

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### Type Members

1. #### abstract type Constant >: Null <: Universe.ConstantApi

   This "virtual" case class represents the reflection interface for literal expressions which can not be further broken down or evaluated, such as "true", "0", "classOf[List]".

2. #### abstract class ConstantApi extends AnyRef

   The API of Constant instances.

3. #### abstract class ConstantExtractor extends AnyRef

   An extractor class to create and pattern match with syntax `Constant(value)` where `value` is the Scala value of the constant.

### Abstract Value Members

1. #### abstract val Constant: Universe.ConstantExtractor

   The constructor/extractor for `Constant` instances.

### Concrete Value Members

1. #### final def !=(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

2. #### final def ##(): Int

   Definition Classes
     AnyRef → Any

3. #### def +(other: String): String

   Implicit information
     This member is added by an implicit conversion from Constants to any2stringadd[Constants] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd

4. #### def ->[B](y: B): (Constants, B)

   Implicit information
     This member is added by an implicit conversion from Constants to ArrowAssoc[Constants] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()

5. #### final def ==(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

6. #### final def asInstanceOf[T0]: T0

   Definition Classes
     Any

7. #### def clone(): AnyRef

   Attributes
     protected[java.lang]
   Definition Classes
     AnyRef
   Annotations
     @throws( ... )

8. #### def ensuring(cond: (Constants) ⇒ Boolean, msg: ⇒ Any): Constants

   Implicit information
     This member is added by an implicit conversion from Constants to Ensuring[Constants] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring

9. #### def ensuring(cond: (Constants) ⇒ Boolean): Constants

   Implicit information
     This member is added by an implicit conversion from Constants to Ensuring[Constants] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring

10. #### def ensuring(cond: Boolean, msg: ⇒ Any): Constants

    Implicit information
      This member is added by an implicit conversion from Constants to Ensuring[Constants] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

11. #### def ensuring(cond: Boolean): Constants

    Implicit information
      This member is added by an implicit conversion from Constants to Ensuring[Constants] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

12. #### final def eq(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

13. #### def equals(arg0: Any): Boolean

    Definition Classes
      AnyRef → Any

14. #### def finalize(): Unit

    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )

15. #### def formatted(fmtstr: String): String

    Implicit information
      This member is added by an implicit conversion from Constants to StringFormat[Constants] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()

16. #### final def getClass(): Class[_]

    Definition Classes
      AnyRef → Any

17. #### def hashCode(): Int

    Definition Classes
      AnyRef → Any

18. #### final def isInstanceOf[T0]: Boolean

    Definition Classes
      Any

19. #### final def ne(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

20. #### final def notify(): Unit

    Definition Classes
      AnyRef

21. #### final def notifyAll(): Unit

    Definition Classes
      AnyRef

22. #### final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
      AnyRef

23. #### def toString(): String

    Definition Classes
      AnyRef → Any

24. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

25. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

26. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

27. #### def →[B](y: B): (Constants, B)

    Implicit information
      This member is added by an implicit conversion from Constants to ArrowAssoc[Constants] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from Constants to any2stringadd[Constants]

### Inherited by implicit conversion StringFormat from Constants to StringFormat[Constants]

### Inherited by implicit conversion Ensuring from Constants to Ensuring[Constants]

### Inherited by implicit conversion ArrowAssoc from Constants to ArrowAssoc[Constants]

### Constants

### API

The methods available for each reflection entity, without the implementation. Since the reflection entities are later overridden by runtime reflection and macros, their API counterparts guarantee a minimum set of methods that are implemented.

### Extractors

Extractors provide the machinery necessary to allow pattern matching and construction of reflection entities that is similar to case classes, although the entities are only abstract types that are later overridden.

### Ungrouped