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 Mirrors extends AnyRef

  EXPERIMENTAL

  EXPERIMENTAL

  This trait provides support for Mirrors in the Scala Reflection API.

  Mirrors are a central part of Scala Reflection. All information provided by reflection is made accessible through Mirrors. Depending on the type of information to be obtained, or the reflective action to be taken, different flavors of mirrors must be used. "Classloader" mirrors can be used to obtain representations of types and members. From a classloader Mirror, it's possible to obtain more specialized "invoker" Mirrors (the most commonly-used mirrors), which implement reflective invocations, such as method/constructor calls and field accesses.

  The two flavors of mirrors:

  • “Classloader” mirrors. These mirrors translate names to symbols (via methods staticClass/staticModule/staticPackage).
  • "Invoker” mirrors. These mirrors implement reflective invocations (via methods MethodMirror.apply, FieldMirror.get, etc). These "invoker" mirrors are the types of mirrors that are most commonly used.

  Compile-time Mirrors

  Compile-time Mirrors make use of only classloader Mirrors to load Symbols by name.

  The entry point to classloader Mirrors is via scala.reflect.macros.blackbox.Context#mirror or scala.reflect.macros.whitebox.Context#mirror. Typical methods which use classloader Mirrors include scala.reflect.api.Mirror#staticClass, scala.reflect.api.Mirror#staticModule, and scala.reflect.api.Mirror#staticPackage. For example:

  import scala.reflect.macros.blackbox.Context
  
  case class Location(filename: String, line: Int, column: Int)
  
  object Macros {
    def currentLocation: Location = macro impl
  
    def impl(c: Context): c.Expr[Location] = {
      import c.universe._
      val pos = c.macroApplication.pos
      val clsLocation = c.mirror.staticModule("Location") // get symbol of "Location" object
      c.Expr(Apply(Ident(clsLocation), List(Literal(Constant(pos.source.path)), Literal(Constant(pos.line)), Literal(Constant(pos.column)))))
    }
  }

  Of Note: There are several high-level alternatives that one can use to avoid having to manually lookup symbols. For example, typeOf[Location.type].termSymbol (or typeOf[Location].typeSymbol if we needed a ClassSymbol), which are type safe since we don’t have to use Strings to lookup the Symbol.

  Runtime Mirrors

  Runtime Mirrors make use of both classloader and invoker Mirrors.

  The entry point to Mirrors for use at runtime is via ru.runtimeMirror(<classloader>), where ru is scala.reflect.runtime.universe.

  The result of a scala.reflect.api.JavaUniverse#runtimeMirror call is a classloader mirror, of type scala.reflect.api.Mirrors#ReflectiveMirror, which can load symbols by names as discussed above (in the “Compile-time” section).

  A classloader mirror can create invoker mirrors, which include: scala.reflect.api.Mirrors#InstanceMirror, scala.reflect.api.Mirrors#MethodMirror, scala.reflect.api.Mirrors#FieldMirror, scala.reflect.api.Mirrors#ClassMirror and scala.reflect.api.Mirrors#ModuleMirror.

  Examples of how these two types of Mirrors interact are available below.

  Types of Mirrors, Their Use Cases & Examples

  scala.reflect.api.Mirrors#ReflectiveMirror. Used for loading Symbols by name, and as an entry point into invoker mirrors. Entry point: val m = ru.runtimeMirror(<classloader>). Example:

  scala> val ru = scala.reflect.runtime.universe
  ru: scala.reflect.api.JavaUniverse = ...
  
  scala> val m = ru.runtimeMirror(getClass.getClassLoader)
  m: reflect.runtime.universe.Mirror = JavaMirror ...

  scala.reflect.api.Mirrors#InstanceMirror. Used for creating invoker Mirrors for methods and fields and for inner classes and inner objects (modules). Entry point: val im = m.reflect(<value>). Example:

  scala> class C { def x = 2 }
  defined class C
  
  scala> val im = m.reflect(new C)
  im: reflect.runtime.universe.InstanceMirror = instance mirror for C@3442299e

  scala.reflect.api.Mirrors#MethodMirror. Used for invoking instance methods (Scala only has instance methods-- methods of objects are instance methods of object instances, obtainable via ModuleMirror.instance). Entry point: val mm = im.reflectMethod(<method symbol>). Example:

  scala> val methodX = typeOf[C].decl(TermName("x")).asMethod
  methodX: reflect.runtime.universe.MethodSymbol = method x
  
  scala> val mm = im.reflectMethod(methodX)
  mm: reflect.runtime.universe.MethodMirror = method mirror for C.x: scala.Int (bound to C@3442299e)
  
  scala> mm()
  res0: Any = 2

  scala.reflect.api.Mirrors#FieldMirror. Used for getting/setting instance fields (Scala only has instance fields-- fields of objects are instance methods of object instances obtainable via ModuleMirror.instance). Entry point: val fm = im.reflectMethod(<field or accessor symbol>). Example:

  scala> class C { val x = 2; val y = 3 }
  defined class C
  
  scala> val m = ru.runtimeMirror(getClass.getClassLoader)
  m: reflect.runtime.universe.Mirror = JavaMirror ...
  
  scala> val im = m.reflect(new C)
  im: reflect.runtime.universe.InstanceMirror = instance mirror for C@5f0c8ac1
  
  scala> val fieldX = typeOf[C].decl(TermName("x")).asTerm.accessed.asTerm
  fieldX: reflect.runtime.universe.TermSymbol = value x
  scala> val fmX = im.reflectField(fieldX)
  fmX: reflect.runtime.universe.FieldMirror = field mirror for C.x (bound to C@5f0c8ac1)
  
  scala> fmX.get
  res0: Any = 2
  
  scala> fmX.set(3) // NOTE: can set an underlying value of an immutable field!
  
  scala> val fieldY = typeOf[C].decl(TermName("y")).asTerm.accessed.asTerm
  fieldY: reflect.runtime.universe.TermSymbol = variable y
  
  scala> val fmY = im.reflectField(fieldY)
  fmY: reflect.runtime.universe.FieldMirror = field mirror for C.y (bound to C@5f0c8ac1)
  
  scala> fmY.get
  res1: Any = 3
  
  scala> fmY.set(4)
  
  scala> fmY.get
  res2: Any = 4

  scala.reflect.api.Mirrors#ClassMirror. Used for creating invoker mirrors for constructors. Entry points: for static classes val cm1 = m.reflectClass(<class symbol>), for inner classes val mm2 = im.reflectClass(<class symbol>). Example:

  scala> case class C(x: Int)
  defined class C
  
  scala> val m = ru.runtimeMirror(getClass.getClassLoader)
  m: reflect.runtime.universe.Mirror = JavaMirror ...
  
  scala> val classC = typeOf[C].typeSymbol.asClass
  
  classC: reflect.runtime.universe.Symbol = class C
  
  scala> val cm = m.reflectClass(classC)
  cm: reflect.runtime.universe.ClassMirror = class mirror for C (bound to null)
  
  scala> val ctorC = typeOf[C].decl(ru.nme.CONSTRUCTOR).asMethod
  ctorC: reflect.runtime.universe.MethodSymbol = constructor C
  
  scala> val ctorm = cm.reflectConstructor(ctorC)
  ctorm: reflect.runtime.universe.MethodMirror = constructor mirror for C.<init>(x: scala.Int): C (bound to null)
  
  scala> ctorm(2)
  res0: Any = C(2)

  scala.reflect.api.Mirrors#ModuleMirror. Used for getting singleton instances of objects. Entry points: for static objects (modules) val mm1 = m.reflectModule(<module symbol>), for inner objects (modules) val mm2 = im.reflectModule(<module symbol>). Example:

  scala> object C { def x = 2 }
  defined module C
  
  scala> val m = ru.runtimeMirror(getClass.getClassLoader)
  m: reflect.runtime.universe.Mirror = JavaMirror ...
  
  scala> val objectC = typeOf[C.type].termSymbol.asModule
  objectC: reflect.runtime.universe.ModuleSymbol = object C
  
  scala> val mm = m.reflectModule(objectC)
  mm: reflect.runtime.universe.ModuleMirror = module mirror for C (bound to null)
  
  scala> val obj = mm.instance
  obj: Any = C$@1005ec04

  For more information about Mirrorss, see the Reflection Guide: Mirrors

  Definition Classes

  api

• ClassMirror
• FieldMirror
• InstanceMirror
• MethodMirror
• Mirror
• ModuleMirror
• ReflectiveMirror
• RuntimeClass
• RuntimeClassApi
• RuntimeMirror
• TemplateMirror

scala.reflect.api.Mirrors

ReflectiveMirror