Packages

•  package root

  Definition Classes

  root

•  package scala

  Definition Classes

  root

•  package reflect

  Definition Classes

  scala

•  package api

  EXPERIMENTAL

  EXPERIMENTAL

  The Scala Reflection API (located in scala-reflect.jar).

  In Scala 2.10.0, the Scala Reflection API and its implementation have an "experimental" status. This means that the API and the docs are not complete and can be changed in binary- and source-incompatible manner in 2.10.1. This also means that the implementation has some known issues.

  The following types are the backbone of the Scala Reflection API, and serve as a good starting point for information about Scala Reflection:

  • scala.reflect.api.Symbols
  • scala.reflect.api.Types
  • scala.reflect.api.Mirrors
  • scala.reflect.api.Universe

  For more information about Scala Reflection, see the Reflection Guide

  Definition Classes

  reflect

•  trait Constants extends AnyRef

  EXPERIMENTAL

  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(TermName(name)).asInstanceOf[LiteralArgument].value
  
    val classRef = jarg("classRef").typeValue
    println(showRaw(classRef))             // TypeRef(ThisType(<empty>), 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://github.com/scala/bug/issues/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
  }

  Definition Classes

  api

• Constant
• ConstantApi
• ConstantExtractor

scala.reflect.api.Constants

ConstantExtractor