Class scala.reflect.macros.Universe

Information about an annotation.

The API of Annotation instances. The main source of information about annotations is the scala.reflect.api.Annotations page.

An extractor class to create and pattern match with syntax Annotation(tpe, scalaArgs, javaArgs). Here, tpe is the annotation type, scalaArgs the payload of Scala annotations, and javaArgs the payload of Java annotations.

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]". Such values become parts of the Scala abstract syntax tree representing the program. The constants correspond to section 6.24 "Constant Expressions" of the Scala Language Specification.

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).

Constants can be matched against and can be constructed directly, as if they were case classes:

assert(Constant(true).value == true)
Constant(true) match {
  case Constant(s: String) =>  println("A string: " + s)
  case Constant(b: Boolean) => println("A boolean value: " + b)
  case Constant(x) =>          println("Something else: " + x)
}

Constant instances can wrap certain kinds of these expressions:

Literals of primitive value classes (Byte, Short, Int, Long, Float, Double, Char, Boolean and Unit) - represented directly as the corresponding typeString literals - represented as instances of the String.References to classes, typically constructed with scala.Predef#classOf - represented as types.References to enumeration values - represented as symbols.

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 RuntimeMirror (the simplest way to get such a mirror is using scala.reflect.runtime.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).

Usage example:

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)) match {
    // Constant is always wrapped into a Literal or LiteralArgument tree node
    case LiteralArgument(ct: Constant) => value
    case _ => sys.error("Not a constant")
  }

  val classRef = jarg("classRef").value.asInstanceOf[Type]
                                         // ideally one should match instead of casting
  println(showRaw(classRef))             // TypeRef(ThisType(<empty>), JavaAnnottee, List())
  println(cm.runtimeClass(classRef))     // class JavaAnnottee

  val enumRef = jarg("enumRef").value.asInstanceOf[Symbol]
                                         // ideally one should match instead of casting
  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
}

The API of Constant instances.

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

Expr wraps an abstract syntax tree and tags it with its type. The main source of information about exprs is the scala.reflect.api.Exprs page.

The API of FlagSet instances. The main source of information about flag sets is the scala.reflect.api.FlagSets page.

An abstract type representing sets of flags (like private, final, etc.) that apply to definition trees and symbols

All possible values that can constitute flag sets. The main source of information about flag sets is the scala.reflect.api.FlagSets page.

Presence of an implicit value of this type in scope indicates that source compatibility with Scala 2.10 has been enabled.

The type of free terms introduced by reification.

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

$SYMACCESSORS

The type of free types introduced by reification.

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

$SYMACCESSORS

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]
  ...
}

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.

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.

The API that all references support

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.

This is an internal implementation class.

A type class that defines a representation of T as a Tree.

A type class that defines a way to extract instance of T from a Tree.

A mirror that reflects the instance parts of a runtime class. See the overview page for details on how to use runtime reflection.

A mirror that reflects a field. See the overview page for details on how to use runtime reflection.

A mirror that reflects a runtime value. See the overview page for details on how to use runtime reflection.

A mirror that reflects a method. See the overview page for details on how to use runtime reflection.

A mirror that reflects a Scala object definition or the static parts of a runtime class. See the overview page for details on how to use runtime reflection.

A mirror that reflects instances and static classes. See the overview page for details on how to use runtime reflection.

Has no special methods. Is here to provides erased identity for RuntimeClass.

The API of a mirror for a reflective universe. See the overview page for details on how to use runtime reflection.

A mirror that reflects the instance or static parts of a runtime class. See the overview page for details on how to use runtime reflection.

The API of Name instances.

Has no special methods. Is here to provides erased identity for TermName.

An extractor class to create and pattern match with syntax TermName(s).

Has no special methods. Is here to provides erased identity for TypeName.

An extractor class to create and pattern match with syntax TypeName(s).

Implicit class that introduces q, tq, cq, pq and fq string interpolators that are also known as quasiquotes. With their help you can easily manipulate Scala reflection ASTs.

The type of member scopes, as in class definitions, for example.

The API that all member scopes support

The base type of all scopes.

The API that all scopes support

Defines standard symbols (and types via its base trait).

Defines standard types.

Defines standard names, common for term and type names: These can be accessed via the nme and tpnme members.

Defines standard term names that can be accessed via the nme member.

Defines standard type names that can be accessed via the tpnme member.

The type of class symbols representing class and trait definitions.

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

Class Symbol defines isXXX test methods such as isPublic or isFinal, params and returnType methods for method symbols, baseClasses for class symbols and so on. Some of these methods don't make sense for certain subclasses of Symbol and return NoSymbol, Nil or other empty values.

The type of method symbols representing def declarations.

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

Class Symbol defines isXXX test methods such as isPublic or isFinal, params and returnType methods for method symbols, baseClasses for class symbols and so on. Some of these methods don't make sense for certain subclasses of Symbol and return NoSymbol, Nil or other empty values.

The type of module symbols representing object declarations.

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

Class Symbol defines isXXX test methods such as isPublic or isFinal, params and returnType methods for method symbols, baseClasses for class symbols and so on. Some of these methods don't make sense for certain subclasses of Symbol and return NoSymbol, Nil or other empty values.

The type of symbols representing declarations.

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

Class Symbol defines isXXX test methods such as isPublic or isFinal, params and returnType methods for method symbols, baseClasses for class symbols and so on. Some of these methods don't make sense for certain subclasses of Symbol and return NoSymbol, Nil or other empty values.

The type of term symbols representing val, var, def, and object declarations as well as packages and value parameters.

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

Class Symbol defines isXXX test methods such as isPublic or isFinal, params and returnType methods for method symbols, baseClasses for class symbols and so on. Some of these methods don't make sense for certain subclasses of Symbol and return NoSymbol, Nil or other empty values.

The type of type symbols representing type, class, and trait declarations, as well as type parameters.

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

Class Symbol defines isXXX test methods such as isPublic or isFinal, params and returnType methods for method symbols, baseClasses for class symbols and so on. Some of these methods don't make sense for certain subclasses of Symbol and return NoSymbol, Nil or other empty values.

Alternatives of patterns.

Eliminated by compiler phases Eliminated by compiler phases patmat (in the new pattern matcher of 2.10) or explicitouter (in the old pre-2.10 pattern matcher), except for occurrences in encoded Switch stmt (i.e. remaining Match(CaseDef(...)))

The API that all alternatives support

An extractor class to create and pattern match with syntax Alternative(trees). This AST node corresponds to the following Scala code:

pat1 | ... | patn

A tree that has an annotation attached to it. Only used for annotated types and annotation ascriptions, annotations on definitions are stored in the Modifiers. Eliminated by typechecker (typedAnnotated), the annotations are then stored in an AnnotatedType.

The API that all annotateds support

An extractor class to create and pattern match with syntax Annotated(annot, arg). This AST node corresponds to the following Scala code:

arg @annot // for types arg: @annot // for exprs

Applied type <tpt> [ <args> ], eliminated by RefCheck

The API that all applied type trees support

An extractor class to create and pattern match with syntax AppliedTypeTree(tpt, args). This AST node corresponds to the following Scala code:

tpt[args]

Should only be used with tpt nodes which are types, i.e. which have isType returning true. Otherwise TypeApply should be used instead.

List[Int] as in val x: List[Int] = ??? // represented as AppliedTypeTree(Ident(<List>), List(TypeTree(<Int>)))

def foo[T] = ??? foo[Int] // represented as TypeApply(Ident(<foo>), List(TypeTree(<Int>)))

Value application

The API that all applies support

An extractor class to create and pattern match with syntax Apply(fun, args). This AST node corresponds to the following Scala code:

fun(args)

For instance:

fun[targs](args)

Is expressed as:

Apply(TypeApply(fun, targs), args)

Assignment

The API that all assigns support

An extractor class to create and pattern match with syntax Assign(lhs, rhs). This AST node corresponds to the following Scala code:

lhs = rhs

Either an assignment or a named argument. Only appears in argument lists, eliminated by compiler phase typecheck (doTypedApply), resurrected by reifier.

The API that all assigns support

An extractor class to create and pattern match with syntax AssignOrNamedArg(lhs, rhs). This AST node corresponds to the following Scala code:

m.f(lhs = rhs)

@annotation(lhs = rhs)

Bind a variable to a rhs pattern.

Eliminated by compiler phases patmat (in the new pattern matcher of 2.10) or explicitouter (in the old pre-2.10 pattern matcher).

The API that all binds support

An extractor class to create and pattern match with syntax Bind(name, body). This AST node corresponds to the following Scala code:

pat*

Block of expressions (semicolon separated expressions)

The API that all blocks support

An extractor class to create and pattern match with syntax Block(stats, expr). This AST node corresponds to the following Scala code:

{ stats; expr }

If the block is empty, the expr is set to Literal(Constant(())).

Case clause in a pattern match. (except for occurrences in switch statements). Eliminated by compiler phases patmat (in the new pattern matcher of 2.10) or explicitouter (in the old pre-2.10 pattern matcher)

The API that all case defs support

An extractor class to create and pattern match with syntax CaseDef(pat, guard, body). This AST node corresponds to the following Scala code:

case pat if guard => body

If the guard is not present, the guard is set to EmptyTree. If the body is not specified, the body is set to Literal(Constant(()))

A class definition.

The API that all class defs support

An extractor class to create and pattern match with syntax ClassDef(mods, name, tparams, impl). This AST node corresponds to the following Scala code:

mods class name [tparams] impl

Where impl stands for:

extends parents { defs }

Intersection type <parent1> with ... with <parentN> { <decls> }, eliminated by RefCheck

The API that all compound type trees support

An extractor class to create and pattern match with syntax CompoundTypeTree(templ). This AST node corresponds to the following Scala code:

parent1 with ... with parentN { refinement }

A method or macro definition.

The API that all def defs support

An extractor class to create and pattern match with syntax DefDef(mods, name, tparams, vparamss, tpt, rhs). This AST node corresponds to the following Scala code:

mods def name[tparams](vparams_1)...(vparams_n): tpt = rhs

If the return type is not specified explicitly (i.e. is meant to be inferred), this is expressed by having tpt set to TypeTree() (but not to an EmptyTree!).

A tree representing a symbol-defining entity: 1) A declaration or a definition (type, class, object, package, val, var, or def) 2) Bind that is used to represent binding occurrences in pattern matches 3) LabelDef that is used internally to represent while loops

The API that all def trees support

Existential type tree node

The API that all existential type trees support

An extractor class to create and pattern match with syntax ExistentialTypeTree(tpt, whereClauses). This AST node corresponds to the following Scala code:

tpt forSome { whereClauses }

Anonymous function, eliminated by compiler phase lambdalift

The API that all functions support

An extractor class to create and pattern match with syntax Function(vparams, body). This AST node corresponds to the following Scala code:

vparams => body

The symbol of a Function is a synthetic TermSymbol. It is the owner of the function's parameters.

Common base class for Apply and TypeApply.

The API that all applies support

A reference to identifier name.

The API that all idents support

An extractor class to create and pattern match with syntax Ident(qual, name). This AST node corresponds to the following Scala code:

name

Type checker converts idents that refer to enclosing fields or methods to selects. For example, name ==> this.name

Conditional expression

The API that all ifs support

An extractor class to create and pattern match with syntax If(cond, thenp, elsep). This AST node corresponds to the following Scala code:

if (cond) thenp else elsep

If the alternative is not present, the elsep is set to Literal(Constant(())).

A common base class for class and object definitions.

The API that all impl defs support

Import clause

The API that all imports support

An extractor class to create and pattern match with syntax Import(expr, selectors). This AST node corresponds to the following Scala code:

import expr.{selectors}

Selectors are a list of ImportSelectors, which conceptually are pairs of names (from, to). The last (and maybe only name) may be a nme.WILDCARD. For instance:

import qual.{x, y => z, _}

Would be represented as:

Import(qual, List(("x", "x"), ("y", "z"), (WILDCARD, null)))

The symbol of an Import is an import symbol @see Symbol.newImport. It's used primarily as a marker to check that the import has been typechecked.

Import selector (not a tree, but a component of the Import tree)

Representation of an imported name its optional rename and their optional positions

Eliminated by typecheck.

The API that all import selectors support

An extractor class to create and pattern match with syntax ImportSelector(name:, namePos, rename, renamePos). This is not an AST node, it is used as a part of the Import node.

A labelled expression. Not expressible in language syntax, but generated by the compiler to simulate while/do-while loops, and also by the pattern matcher.

The label acts much like a nested function, where params represents the incoming parameters. The symbol given to the LabelDef should have a MethodType, as if it were a nested function.

Jumps are apply nodes attributed with a label's symbol. The arguments from the apply node will be passed to the label and assigned to the Idents.

Forward jumps within a block are allowed.

The API that all label defs support

An extractor class to create and pattern match with syntax LabelDef(name, params, rhs).

This AST node does not have direct correspondence to Scala code. It is used for tailcalls and like. For example, while/do are desugared to label defs as follows:

while (cond) body ==> LabelDef($L, List(), if (cond) { body; L$() } else ())

do body while (cond) ==> LabelDef($L, List(), body; if (cond) L$() else ())

Literal

The API that all literals support

An extractor class to create and pattern match with syntax Literal(value). This AST node corresponds to the following Scala code:

value

- Pattern matching expression (before compiler phase explicitouter before 2.10 / patmat from 2.10)

Switch statements (after compiler phase explicitouter before 2.10 / patmat from 2.10)

After compiler phase explicitouter before 2.10 / patmat from 2.10, cases will satisfy the following constraints:

all guards are EmptyTree,all patterns will be either Literal(Constant(x:Int)) or Alternative(lit|...|lit)except for an "otherwise" branch, which has pattern Ident(nme.WILDCARD)

The API that all matches support

An extractor class to create and pattern match with syntax Match(selector, cases). This AST node corresponds to the following Scala code:

selector match { cases }

Match is also used in pattern matching assignments like val (foo, bar) = baz.

Common base class for all member definitions: types, classes, objects, packages, vals and vars, defs.

The API that all member defs support

The API that all Modifiers support

An extractor class to create and pattern match with syntax Modifiers(flags, privateWithin, annotations). Modifiers encapsulate flags, visibility annotations and Scala annotations for member definitions.

An object definition, e.g. object Foo. Internally, objects are quite frequently called modules to reduce ambiguity. Eliminated by compiler phase refcheck.

The API that all module defs support

An extractor class to create and pattern match with syntax ModuleDef(mods, name, impl). This AST node corresponds to the following Scala code:

mods object name impl

Where impl stands for:

extends parents { defs }

A tree that carries a name, e.g. by defining it (DefTree) or by referring to it (RefTree).

The API that all name trees support

Object instantiation

The API that all news support

An extractor class to create and pattern match with syntax New(tpt). This AST node corresponds to the following Scala code:

new T

This node always occurs in the following context:

(new tpt).<init>[targs](args)

For example, an AST representation of:

new Example[Int](2)(3)

is the following code:

Apply( Apply( TypeApply( Select(New(TypeTree(typeOf[Example])), nme.CONSTRUCTOR) TypeTree(typeOf[Int])), List(Literal(Constant(2)))), List(Literal(Constant(3))))

A packaging, such as package pid { stats }

The API that all package defs support

An extractor class to create and pattern match with syntax PackageDef(pid, stats). This AST node corresponds to the following Scala code:

package pid { stats }

A tree which references a symbol-carrying entity. References one, as opposed to defining one; definitions are in DefTrees.

The API that all ref trees support

An extractor class to create and pattern match with syntax RefTree(qual, name). This AST node corresponds to either Ident, Select or SelectFromTypeTree.

Return expression

The API that all returns support

An extractor class to create and pattern match with syntax Return(expr). This AST node corresponds to the following Scala code:

return expr

The symbol of a Return node is the enclosing method.

A member selection <qualifier> . <name>

The API that all selects support

An extractor class to create and pattern match with syntax Select(qual, name). This AST node corresponds to the following Scala code:

qualifier.selector

Should only be used with qualifier nodes which are terms, i.e. which have isTerm returning true. Otherwise SelectFromTypeTree should be used instead.

foo.Bar // represented as Select(Ident(<foo>), <Bar>) Foo#Bar // represented as SelectFromTypeTree(Ident(<Foo>), <Bar>)

Type selection <qualifier> # <name>, eliminated by RefCheck

The API that all selects from type trees support

An extractor class to create and pattern match with syntax SelectFromTypeTree(qualifier, name). This AST node corresponds to the following Scala code:

qualifier # selector

Note: a path-dependent type p.T is expressed as p.type # T

Should only be used with qualifier nodes which are types, i.e. which have isType returning true. Otherwise Select should be used instead.

Foo#Bar // represented as SelectFromTypeTree(Ident(<Foo>), <Bar>) foo.Bar // represented as Select(Ident(<foo>), <Bar>)

Singleton type, eliminated by RefCheck

The API that all singleton type trees support

An extractor class to create and pattern match with syntax SingletonTypeTree(ref). This AST node corresponds to the following Scala code:

ref.type

Repetition of pattern.

Eliminated by compiler phases patmat (in the new pattern matcher of 2.10) or explicitouter (in the old pre-2.10 pattern matcher).

The API that all stars support

An extractor class to create and pattern match with syntax Star(elem). This AST node corresponds to the following Scala code:

pat*

Super reference, where qual is the corresponding this reference. A super reference C.super[M] is represented as Super(This(C), M).

The API that all supers support

An extractor class to create and pattern match with syntax Super(qual, mix). This AST node corresponds to the following Scala code:

C.super[M]

Which is represented as:

Super(This(C), M)

If mix is empty, it is tpnme.EMPTY.

The symbol of a Super is the class _from_ which the super reference is made. For instance in C.super(...), it would be C.

A tree that carries a symbol, e.g. by defining it (DefTree) or by referring to it (RefTree). Such trees start their life naked, returning NoSymbol, but after being typechecked without errors they hold non-empty symbols.

The API that all sym trees support

Instantiation template of a class or trait

The API that all templates support

An extractor class to create and pattern match with syntax Template(parents, self, body). This AST node corresponds to the following Scala code:

extends parents { self => body }

In case when the self-type annotation is missing, it is represented as an empty value definition with nme.WILDCARD as name and NoType as type.

The symbol of a template is a local dummy. @see Symbol.newLocalDummy The owner of the local dummy is the enclosing trait or class. The local dummy is itself the owner of any local blocks. For example:

class C { def foo { // owner is C def bar // owner is local dummy } }

A tree for a term. Not all trees representing terms are TermTrees; use isTerm to reliably identify terms.

The API that all term trees support

Self reference

The API that all thises support

An extractor class to create and pattern match with syntax This(qual). This AST node corresponds to the following Scala code:

qual.this

The symbol of a This is the class to which the this refers. For instance in C.this, it would be C.

Throw expression

The API that all tries support

An extractor class to create and pattern match with syntax Throw(expr). This AST node corresponds to the following Scala code:

throw expr

A class that implement a default tree transformation strategy: breadth-first component-wise cloning.

A class that implement a default tree traversal strategy: breadth-first component-wise.

The type of Scala abstract syntax trees.

The API that all trees support. The main source of information about trees is the scala.reflect.api.Trees page.

The type of standard (lazy) tree copiers.

The API of a tree copier.

Try catch node

The API that all tries support

An extractor class to create and pattern match with syntax Try(block, catches, finalizer). This AST node corresponds to the following Scala code:

try block catch { catches } finally finalizer

If the finalizer is not present, the finalizer is set to EmptyTree.

A tree for a type. Not all trees representing types are TypTrees; use isType to reliably identify types.

The API that all typ trees support

Explicit type application.

The API that all type applies support

An extractor class to create and pattern match with syntax TypeApply(fun, args). This AST node corresponds to the following Scala code:

fun[args]

Should only be used with fun nodes which are terms, i.e. which have isTerm returning true. Otherwise AppliedTypeTree should be used instead.

def foo[T] = ??? foo[Int] // represented as TypeApply(Ident(<foo>), List(TypeTree(<Int>)))

List[Int] as in val x: List[Int] = ??? // represented as AppliedTypeTree(Ident(<List>), List(TypeTree(<Int>)))

Type bounds tree node

The API that all type bound trees support

An extractor class to create and pattern match with syntax TypeBoundsTree(lo, hi). This AST node corresponds to the following Scala code:

>: lo <: hi

An abstract type, a type parameter, or a type alias. Eliminated by erasure.

The API that all type defs support

An extractor class to create and pattern match with syntax TypeDef(mods, name, tparams, rhs). This AST node corresponds to the following Scala code:

mods type name[tparams] = rhs

mods type name[tparams] >: lo <: hi

First usage illustrates TypeDefs representing type aliases and type parameters. Second usage illustrates TypeDefs representing abstract types, where lo and hi are both TypeBoundsTrees and Modifier.deferred is set in mods.

A synthetic tree holding an arbitrary type. Not to be confused with with TypTree, the trait for trees that are only used for type trees. TypeTree's are inserted in several places, but most notably in RefCheck, where the arbitrary type trees are all replaced by TypeTree's.

The API that all type trees support

An extractor class to create and pattern match with syntax TypeTree(). This AST node does not have direct correspondence to Scala code, and is emitted by everywhere when we want to wrap a Type in a Tree.

Type annotation, eliminated by compiler phase cleanup

The API that all typeds support

An extractor class to create and pattern match with syntax Typed(expr, tpt). This AST node corresponds to the following Scala code:

expr: tpt

Used to represent unapply methods in pattern matching.

For example:

2 match { case Foo(x) => x }

Is represented as:

Match(
  Literal(Constant(2)),
  List(
    CaseDef(
      UnApply(
        // a dummy node that carries the type of unapplication to patmat
        // the <unapply-selector> here doesn't have an underlying symbol
        // it only has a type assigned, therefore after `untypecheck` this tree is no longer typeable
        Apply(Select(Ident(Foo), TermName("unapply")), List(Ident(TermName("<unapply-selector>")))),
        // arguments of the unapply => nothing synthetic here
        List(Bind(TermName("x"), Ident(nme.WILDCARD)))),
      EmptyTree,
      Ident(TermName("x")))))

Introduced by typer. Eliminated by compiler phases patmat (in the new pattern matcher of 2.10) or explicitouter (in the old pre-2.10 pattern matcher).

The API that all unapplies support

An extractor class to create and pattern match with syntax UnApply(fun, args). This AST node does not have direct correspondence to Scala code, and is introduced when typechecking pattern matches and try blocks.

Broadly speaking, a value definition. All these are encoded as ValDefs:

immutable values, e.g. "val x"mutable values, e.g. "var x" - the MUTABLE flag set in modslazy values, e.g. "lazy val x" - the LAZY flag set in modsmethod parameters, see vparamss in scala.reflect.api.Trees#DefDef - the PARAM flag is set in modsexplicit self-types, e.g. class A { self: Bar => }

The API that all val defs support

An extractor class to create and pattern match with syntax ValDef(mods, name, tpt, rhs). This AST node corresponds to any of the following Scala code:

mods val name: tpt = rhs

mods var name: tpt = rhs

mods name: tpt = rhs // in signatures of function and method definitions

self: Bar => // self-types

If the type of a value is not specified explicitly (i.e. is meant to be inferred), this is expressed by having tpt set to TypeTree() (but not to an EmptyTree!).

A common base class for ValDefs and DefDefs.

The API that all val defs and def defs support

A TypeTag is a scala.reflect.api.TypeTags#WeakTypeTag with the additional static guarantee that all type references are concrete, i.e. it does not contain any references to unresolved type parameters or abstract types.

If an implicit value of type WeakTypeTag[T] is required, the compiler will create one, and the reflective representation of T can be accessed via the tpe field. Components of T can be references to type parameters or abstract types. Note that WeakTypeTag makes an effort to be as concrete as possible, i.e. if TypeTags are available for the referenced type arguments or abstract types, they are used to embed the concrete types into the WeakTypeTag. Otherwise the WeakTypeTag will contain a reference to an abstract type. This behavior can be useful, when one expects T to be perhaps be partially abstract, but requires special care to handle this case. However, if T is expected to be fully known, use scala.reflect.api.TypeTags#TypeTag instead, which statically guarantees this property.

For more information about TypeTags, see the Reflection Guide: TypeTags

The AnnotatedType type signature is used for annotated types of the for <type> @<annotation>.

The API that all annotated types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax AnnotatedType(annotations, underlying). Here, annotations are the annotations decorating the underlying type underlying. selfSym is a symbol representing the annotated type itself.

BoundedWildcardTypes, used only during type inference, are created in two places:

If the expected type of an expression is an existential type, its hidden symbols are replaced with bounded wildcards. 2. When an implicit conversion is being sought based in part on the name of a method in the converted type, a HasMethodMatching type is created: a MethodType with parameters typed as BoundedWildcardTypes.

The API that all this types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax BoundedWildcardTypeExtractor(bounds) with bounds denoting the type bounds.

The ClassInfo type signature is used to define parents and declarations of classes, traits, and objects. If a class, trait, or object C is declared like this

C extends P_1 with ... with P_m { D_1; ...; D_n}

its ClassInfo type has the following form:

ClassInfo(List(P_1, ..., P_m), Scope(D_1, ..., D_n), C)

The API that all class info types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax ClassInfo(parents, decls, clazz) Here, parents is the list of parent types of the class, decls is the scope containing all declarations in the class, and clazz is the symbol of the class itself.

A subtype of Type representing refined types as well as ClassInfo signatures.

Has no special methods. Is here to provides erased identity for CompoundType.

The ConstantType type is not directly written in user programs, but arises as the type of a constant. The REPL expresses constant types like Int(11). Here are some constants with their types:

1           ConstantType(Constant(1))
"abc"       ConstantType(Constant("abc"))

The API that all constant types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax ConstantType(constant) Here, constant is the constant value represented by the type.

The ExistentialType type signature is used for existential types and wildcard types.

The API that all existential types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax ExistentialType(quantified, underlying). Here, quantified are the type variables bound by the existential type and underlying is the type that's existentially quantified.

The MethodType type signature is used to indicate parameters and result type of a method

The API that all method types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax MethodType(params, restpe) Here, params is a potentially empty list of parameter symbols of the method, and restpe is the result type of the method. If the method is curried, restpe would be another MethodType. Note: MethodType(Nil, Int) would be the type of a method defined with an empty parameter list.

def f(): Int

If the method is completely parameterless, as in

def f: Int

its type is a NullaryMethodType.

The NullaryMethodType type signature is used for parameterless methods with declarations of the form def foo: T

The API that all nullary method types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax NullaryMethodType(resultType). Here, resultType is the result type of the parameterless method.

The PolyType type signature is used for polymorphic methods that have at least one type parameter.

The API that all polymorphic types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax PolyType(typeParams, resultType). Here, typeParams are the type parameters of the method and resultType is the type signature following the type parameters.

The RefinedType type defines types of any of the forms on the left, with their RefinedType representations to the right.

P_1 with ... with P_m { D_1; ...; D_n}      RefinedType(List(P_1, ..., P_m), Scope(D_1, ..., D_n))
P_1 with ... with P_m                       RefinedType(List(P_1, ..., P_m), Scope())
{ D_1; ...; D_n}                            RefinedType(List(AnyRef), Scope(D_1, ..., D_n))

The API that all refined types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax RefinedType(parents, decls) Here, parents is the list of parent types of the class, and decls is the scope containing all declarations in the class.

The SingleType type describes types of any of the forms on the left, with their TypeRef representations to the right.

(T # x).type             SingleType(T, x)
p.x.type                 SingleType(p.type, x)
x.type                   SingleType(NoPrefix, x)

The API that all single types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax SingleType(pre, sym) Here, pre is the prefix of the single-type, and sym is the stable value symbol referred to by the single-type.

The type of Scala singleton types, i.e., types that are inhabited by only one nun-null value. These include types of the forms

C.this.type
C.super.type
x.type

as well as constant types.

Has no special methods. Is here to provides erased identity for SingletonType.

The SuperType type is not directly written, but arises when C.super is used as a prefix in a TypeRef or SingleType. It's internal presentation is

SuperType(thistpe, supertpe)

Here, thistpe is the type of the corresponding this-type. For instance, in the type arising from C.super, the thistpe part would be ThisType(C). supertpe is the type of the super class referred to by the super.

The API that all super types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax SingleType(thistpe, supertpe)

A singleton type that describes types of the form on the left with the corresponding ThisType representation to the right:

C.this.type             ThisType(C)

The API that all this types support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax ThisType(sym) where sym is the class prefix of the this type.

The type of Scala types, and also Scala type signatures. (No difference is internally made between the two).

The API of types. The main source of information about types is the scala.reflect.api.Types page.

The TypeBounds type signature is used to indicate lower and upper type bounds of type parameters and abstract types. It is not a first-class type. If an abstract type or type parameter is declared with any of the forms on the left, its type signature is the TypeBounds type on the right.

T >: L <: U               TypeBounds(L, U)
T >: L                    TypeBounds(L, Any)
T <: U                    TypeBounds(Nothing, U)

The API that all type bounds support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax TypeBound(lower, upper) Here, lower is the lower bound of the TypeBounds pair, and upper is the upper bound.

The TypeRef type describes types of any of the forms on the left, with their TypeRef representations to the right.

T # C[T_1, ..., T_n]      TypeRef(T, C, List(T_1, ..., T_n))
p.C[T_1, ..., T_n]        TypeRef(p.type, C, List(T_1, ..., T_n))
C[T_1, ..., T_n]          TypeRef(NoPrefix, C, List(T_1, ..., T_n))
T # C                     TypeRef(T, C, Nil)
p.C                       TypeRef(p.type, C, Nil)
C                         TypeRef(NoPrefix, C, Nil)

The API that all type refs support. The main source of information about types is the scala.reflect.api.Types page.

An extractor class to create and pattern match with syntax TypeRef(pre, sym, args) Here, pre is the prefix of the type reference, sym is the symbol referred to by the type reference, and args is a possible empty list of type arguments.

The base type of all mirrors of this universe.

This abstract type conforms the base interface for all mirrors defined in scala.reflect.api.Mirror and is gradually refined in specific universes (e.g. Mirror of a scala.reflect.api.JavaUniverse is capable of reflection).

The type of tree modifiers (not a tree, but rather part of DefTrees).

The abstract type of names.

Defines a universe-specific notion of positions. The main documentation entry about positions is located at scala.reflect.api.Position.

Abstracts the runtime representation of a class on the underlying platform.

The abstract type of names representing types.

The abstract type of names representing terms.

An array argument to a Java annotation as in @Target(value={TYPE,FIELD,METHOD,PARAMETER})

API of ArrayArgument instances. The main source of information about annotations is the scala.reflect.api.Annotations page.

An extractor class to create and pattern match with syntax ArrayArgument(args) where args is the argument array.

A Java annotation argument

Has no special methods. Is here to provides erased identity for CompoundType.

A literal argument to a Java annotation as "use X instead" in @Deprecated("use X instead")

The API of LiteralArgument instances. The main source of information about annotations is the scala.reflect.api.Annotations page.

An extractor class to create and pattern match with syntax LiteralArgument(value) where value is the constant argument.

A nested annotation argument to a Java annotation as @Nested in @Outer(@Nested).

API of NestedArgument instances. The main source of information about annotations is the scala.reflect.api.Annotations page.

An extractor class to create and pattern match with syntax NestedArgument(annotation) where annotation is the nested annotation.

The type of compilation units.

Compilation unit describes a unit of work of the compilation run. It provides such information as file name, textual representation of the unit and the underlying AST.

The type of compilation runs.

Compilation run uniquely identifies current invocation of the compiler (e.g. can be used to implement per-run caches for macros) and provides access to units of work of the invocation (currently processed unit of work and the list of all units).