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/Scala 2.13 Reflection

Trait scala.reflect.api.Internals

trait Internals extends AnyRef

EXPERIMENTAL

This trait assembles APIs occasionally necessary for performing low-level operations on reflection artifacts. See Internals#InternalApi for more information about nature, usefulness and compatibility guarantees of these APIs.

Self Type
Universe
Source
Internals.scala
Linear Supertypes
AnyRef, Any
Known Subclasses
JavaUniverse, Universe, Universe

Type Members

abstract type FreeTermSymbol >: Null <: Universe.FreeTermSymbolApi with Universe.TermSymbol

trait FreeTermSymbolApi extends Universe.TermSymbolApi

The API of free term symbols. The main source of information about symbols is the Symbols page.

$SYMACCESSORS

abstract type FreeTypeSymbol >: Null <: Universe.FreeTypeSymbolApi with Universe.TypeSymbol

trait FreeTypeSymbolApi extends Universe.TypeSymbolApi

The API of free type symbols. The main source of information about symbols is the Symbols page.

$SYMACCESSORS

trait Importer extends AnyRef

This trait provides support for importers, a facility to migrate reflection artifacts between universes. Note: this trait should typically be used only rarely.

Reflection artifacts, such as Symbols and Types, are contained in Universes. Typically all processing happens within a single Universe (e.g. a compile-time macro Universe or a runtime reflection Universe), but sometimes there is a need to migrate artifacts from one Universe to another. For example, runtime compilation works by importing runtime reflection trees into a runtime compiler universe, compiling the importees and exporting the result back.

Reflection artifacts are firmly grounded in their Universes, which is reflected by the fact that types of artifacts from different universes are not compatible. By using Importers, however, they be imported from one universe into another. For example, to import foo.bar.Baz from the source Universe to the target Universe, an importer will first check whether the entire owner chain exists in the target Universe. If it does, then nothing else will be done. Otherwise, the importer will recreate the entire owner chain and will import the corresponding type signatures into the target Universe.

Since importers match Symbol tables of the source and the target Universes using plain string names, it is programmer's responsibility to make sure that imports don't distort semantics, e.g., that foo.bar.Baz in the source Universe means the same that foo.bar.Baz does in the target Universe.

Example

Here's how one might implement a macro that performs compile-time evaluation of its argument by using a runtime compiler to compile and evaluate a tree that belongs to a compile-time compiler:

def staticEval[T](x: T) = macro staticEval[T]

def staticEval[T](c: scala.reflect.macros.blackbox.Context)(x: c.Expr[T]) = {
  // creates a runtime reflection universe to host runtime compilation
  import scala.reflect.runtime.{universe => ru}
  val mirror = ru.runtimeMirror(c.libraryClassLoader)
  import scala.tools.reflect.ToolBox
  val toolBox = mirror.mkToolBox()

  // runtime reflection universe and compile-time macro universe are different
  // therefore an importer is needed to bridge them
  // currently mkImporter requires a cast to correctly assign the path-dependent types
  val importer0 = ru.internal.mkImporter(c.universe)
  val importer = importer0.asInstanceOf[ru.internal.Importer { val from: c.universe.type }]

  // the created importer is used to turn a compiler tree into a runtime compiler tree
  // both compilers use the same classpath, so semantics remains intact
  val imported = importer.importTree(tree)

  // after the tree is imported, it can be evaluated as usual
  val tree = toolBox.untypecheck(imported.duplicate)
  val valueOfX = toolBox.eval(imported).asInstanceOf[T]
  ...
}

abstract type Internal <: Universe.InternalApi

See also

InternalApi

trait InternalApi extends AnyRef

Reflection API exhibits a tension inherent to experimental things: on the one hand we want it to grow into a beautiful and robust API, but on the other hand we have to deal with immaturity of underlying mechanisms by providing not very pretty solutions to enable important use cases.

In Scala 2.10, which was our first stab at reflection API, we didn't have a systematic approach to dealing with this tension, sometimes exposing too much of internals (e.g. Symbol.deSkolemize) and sometimes exposing too little (e.g. there's still no facility to change owners, to do typing transformations, etc). This resulted in certain confusion with some internal APIs living among public ones, scaring the newcomers, and some internal APIs only available via casting, which requires intimate knowledge of the compiler and breaks compatibility guarantees.

This led to creation of the internal API module for the reflection API, which provides advanced APIs necessary for macros that push boundaries of the state of the art, clearly demarcating them from the more or less straightforward rest and providing compatibility guarantees on par with the rest of the reflection API (full compatibility within minor releases, best effort towards backward compatibility within major releases, clear replacement path in case of rare incompatible changes in major releases).

The internal module itself (the value that implements InternalApi) isn't defined here, in scala.reflect.api.Universe, but is provided on per-implementation basis. Runtime API endpoint (scala.reflect.runtime.universe) provides universe.compat: InternalApi, whereas compile-time API endpoints (instances of scala.reflect.macros.Context) provide c.compat: ContextInternalApi, which extends InternalApi with additional universe-specific and context-specific functionality.

abstract type ReferenceToBoxed >: Null <: Universe.ReferenceToBoxedApi with Universe.TermTree

Marks underlying reference to id as boxed.

Precondition: id must refer to a captured variable A reference such marked will refer to the boxed entity, no dereferencing with `.elem` is done on it. This tree node can be emitted by macros such as reify that call referenceCapturedVariable. It is eliminated in LambdaLift, where the boxing conversion takes place.

trait ReferenceToBoxedApi extends Universe.TermTreeApi

abstract class ReferenceToBoxedExtractor extends AnyRef

An extractor class to create and pattern match with syntax ReferenceToBoxed(ident). This AST node does not have direct correspondence to Scala code, and is emitted by macros to reference capture vars directly without going through elem.

For example:

var x = ... fun { x }

Will emit:

Ident(x)

Which gets transformed to:

Select(Ident(x), "elem")

If ReferenceToBoxed were used instead of Ident, no transformation would be performed.

trait ReificationSupportApi extends AnyRef

Abstract Value Members

implicit abstract val FreeTermSymbolTag: ClassTag[Universe.FreeTermSymbol]

Tag that preserves the identity of FreeTermSymbol in the face of erasure. Can be used for pattern matching, instance tests, serialization and the like.

implicit abstract val FreeTypeSymbolTag: ClassTag[Universe.FreeTypeSymbol]

Tag that preserves the identity of FreeTermSymbol in the face of erasure. Can be used for pattern matching, instance tests, serialization and the like.

abstract val ReferenceToBoxed: Universe.ReferenceToBoxedExtractor

implicit abstract val ReferenceToBoxedTag: ClassTag[Universe.ReferenceToBoxed]

Tag that preserves the identity of ReferenceToBoxed in the face of erasure. Can be used for pattern matching, instance tests, serialization and the like.

abstract val internal: Universe.Internal

See also

InternalApi

abstract val compat: Universe.Compat

Provides enrichments to ensure source compatibility between Scala 2.10 and Scala 2.11. If in your reflective program for Scala 2.10 you've used something that's now become an internal API, a single compat._ import will fix things for you.

Annotations
@deprecated
Deprecated

(Since version 2.13.0) compatibility with Scala 2.10 EOL

Concrete Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any

final def ##(): Int

Definition Classes
AnyRef → Any

def +(other: String): String

Implicit
This member is added by an implicit conversion from Internals toany2stringadd[Internals] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

def ->[B](y: B): (Internals, B)

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

final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any

final def asInstanceOf[T0]: T0

Definition Classes
Any

def clone(): AnyRef

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

def ensuring(cond: (Internals) => Boolean, msg: => Any): Internals

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

def ensuring(cond: (Internals) => Boolean): Internals

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

def ensuring(cond: Boolean, msg: => Any): Internals

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

def ensuring(cond: Boolean): Internals

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

final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef

def equals(arg0: AnyRef): Boolean

Definition Classes
AnyRef → Any

def finalize(): Unit

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

def formatted(fmtstr: String): String

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

final def getClass(): Class[_ <: AnyRef]

Definition Classes
AnyRef → Any
Annotations
@native()

def hashCode(): Int

Definition Classes
AnyRef → Any
Annotations
@native()

final def isInstanceOf[T0]: Boolean

Definition Classes
Any

final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef

final def notify(): Unit

Definition Classes
AnyRef
Annotations
@native()

final def notifyAll(): Unit

Definition Classes
AnyRef
Annotations
@native()

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def toString(): String

Definition Classes
AnyRef → Any

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

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

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala-reflect/scala/reflect/api/Internals.html