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/Scala 2.12 Reflection

Trait scala.reflect.api.Printers

trait Printers extends AnyRef

EXPERIMENTAL

Utilities for nicely printing scala.reflect.api.Trees and scala.reflect.api.Types.

Printing Trees

The method show displays the "prettified" representation of reflection artifacts. This representation provides one with the desugared Java representation of Scala code. For example:

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> def tree = reify{ final class C { def x = 2 } }.tree
tree: reflect.runtime.universe.Tree

scala> show(tree)
res0: String =
{
  final class C extends AnyRef {
    def <init>() = {
      super.<init>();
      ()
    };
    def x = 2
  };
  ()
}

The method showRaw displays internal structure of a given reflection object as a Scala abstract syntax tree (AST), the representation that the Scala typechecker operates on.

Note, that while this representation appears to generate correct trees that one might think would be possible to use in a macro implementation, this is not usually the case. Symbols aren't fully represented (only their names are). Thus, this method is best-suited for use simply inspecting ASTs given some valid Scala code.

scala> showRaw(tree)
res1: String = Block(List(
  ClassDef(Modifiers(FINAL), TypeName("C"), List(), Template(
    List(Ident(TypeName("AnyRef"))),
    noSelfType,
    List(
      DefDef(Modifiers(), nme.CONSTRUCTOR, List(), List(List()), TypeTree(),
        Block(List(
          Apply(Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR), List())),
          Literal(Constant(())))),
      DefDef(Modifiers(), TermName("x"), List(), List(), TypeTree(),
        Literal(Constant(2))))))),
  Literal(Constant(())))

The method showRaw can also print scala.reflect.api.Types next to the artifacts being inspected

scala> import scala.tools.reflect.ToolBox // requires scala-compiler.jar
import scala.tools.reflect.ToolBox

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

scala> showRaw(cm.mkToolBox().typecheck(tree), printTypes = true)
res2: String = Block[1](List(
  ClassDef[2](Modifiers(FINAL), TypeName("C"), List(), Template[3](
    List(Ident[4](TypeName("AnyRef"))),
    noSelfType,
    List(
      DefDef[2](Modifiers(), nme.CONSTRUCTOR, List(), List(List()), TypeTree[3](),
        Block[1](List(
          Apply[4](Select[5](Super[6](This[3](TypeName("C")), tpnme.EMPTY), ...))),
          Literal[1](Constant(())))),
      DefDef[2](Modifiers(), TermName("x"), List(), List(), TypeTree[7](),
        Literal[8](Constant(2))))))),
  Literal[1](Constant(())))
[1] TypeRef(ThisType(scala), scala.Unit, List())
[2] NoType
[3] TypeRef(NoPrefix, TypeName("C"), List())
[4] TypeRef(ThisType(java.lang), java.lang.Object, List())
[5] MethodType(List(), TypeRef(ThisType(java.lang), java.lang.Object, List()))
[6] SuperType(ThisType(TypeName("C")), TypeRef(... java.lang.Object ...))
[7] TypeRef(ThisType(scala), scala.Int, List())
[8] ConstantType(Constant(2))
Printing Types

The method show

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> def tpe = typeOf[{ def x: Int; val y: List[Int] }]
tpe: reflect.runtime.universe.Type

scala> show(tpe)
res0: String = scala.AnyRef{def x: Int; val y: scala.List[Int]}

Like the method showRaw for scala.reflect.api.Trees, showRaw for scala.reflect.api.Types provides a visualization of the Scala AST operated on by the Scala typechecker.

// showRaw has already been discussed above
scala> showRaw(tpe)
res1: String = RefinedType(
  List(TypeRef(ThisType(scala), TypeName("AnyRef"), List())),
  Scope(
    TermName("x"),
    TermName("y")))

printIds and/or printKinds can additionally be supplied as arguments in a call to showRaw which additionally shows the unique identifiers of symbols.

scala> showRaw(tpe, printIds = true, printKinds = true)
res2: String = RefinedType(
  List(TypeRef(ThisType(scala#2043#PK), TypeName("AnyRef")#691#TPE, List())),
  Scope(
    TermName("x")#2540#METH,
    TermName("y")#2541#GET))

For more details about Printers and other aspects of Scala reflection, see the Reflection Guide

Self Type
Universe
Source
Printers.scala
Linear Supertypes
Known Subclasses

Type Members

case class BooleanFlag(value: Option[Boolean]) extends Product with Serializable

trait TreePrinter extends AnyRef

Attributes
protected

Abstract Value Members

abstract def newCodePrinter(out: PrintWriter, tree: Universe.Tree, printRootPkg: Boolean): Universe.TreePrinter

Hook to define what showCode(...) means.

Attributes
protected

abstract def newRawTreePrinter(out: PrintWriter): Universe.TreePrinter

Hook to define what showRaw(...) means.

Attributes
protected

abstract def newTreePrinter(out: PrintWriter): Universe.TreePrinter

Hook to define what show(...) means.

Attributes
protected

abstract def show(position: Universe.Position): String

abstract def show(flags: Universe.FlagSet): String

abstract def show(name: Universe.Name): String

abstract def showDecl(sym: Universe.Symbol): String

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 Printers to any2stringadd[Printers] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

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

Implicit
This member is added by an implicit conversion from Printers to ArrowAssoc[Printers] 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[lang]
Definition Classes
AnyRef
Annotations
@throws( ... ) @native()

def ensuring(cond: (Printers) ⇒ Boolean, msg: ⇒ Any): Printers

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

def ensuring(cond: (Printers) ⇒ Boolean): Printers

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

def ensuring(cond: Boolean, msg: ⇒ Any): Printers

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

def ensuring(cond: Boolean): Printers

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

final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef

def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any

def finalize(): Unit

Attributes
protected[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 Printers to StringFormat[Printers] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()

final def getClass(): Class[_]

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()

def render(what: Any, mkPrinter: (PrintWriter) ⇒ Universe.TreePrinter, printTypes: Universe.BooleanFlag = None, printIds: Universe.BooleanFlag = None, printOwners: Universe.BooleanFlag = None, printKinds: Universe.BooleanFlag = None, printMirrors: Universe.BooleanFlag = None, printPositions: Universe.BooleanFlag = None): String

Attributes
protected

def show(any: Any, printTypes: Universe.BooleanFlag = None, printIds: Universe.BooleanFlag = None, printOwners: Universe.BooleanFlag = None, printKinds: Universe.BooleanFlag = None, printMirrors: Universe.BooleanFlag = None, printPositions: Universe.BooleanFlag = None): String

def showCode(tree: Universe.Tree, printTypes: Universe.BooleanFlag = None, printIds: Universe.BooleanFlag = None, printOwners: Universe.BooleanFlag = None, printPositions: Universe.BooleanFlag = None, printRootPkg: Boolean = false): String

Renders the code of the passed tree, so that: 1) it can be later compiled by scalac retaining the same meaning, 2) it looks pretty. #1 is available for unattributed trees and attributed trees #2 is more or less okay indentation-wise, but at the moment there's a lot of desugaring left in place, and that's what we plan to improve in the future. printTypes, printIds, printPositions options have the same meaning as for TreePrinter printRootPkg option is available only for attributed trees.

def showRaw(position: Universe.Position): String

def showRaw(flags: Universe.FlagSet): String

def showRaw(name: Universe.Name): String

def showRaw(any: Any, printTypes: Universe.BooleanFlag = None, printIds: Universe.BooleanFlag = None, printOwners: Universe.BooleanFlag = None, printKinds: Universe.BooleanFlag = None, printMirrors: Universe.BooleanFlag = None, printPositions: Universe.BooleanFlag = None): String

final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef

def toString(): String

Definition Classes
AnyRef → Any

def treeToString(tree: Universe.Tree): String

By default trees are printed with show

Attributes
protected

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

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

Definition Classes
AnyRef
Annotations
@throws( ... )

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... ) @native()

def [B](y: B): (Printers, B)

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

object BooleanFlag extends Serializable

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.12.9/scala-reflect/scala/reflect/api/Printers.html