Packages

trait Symbols extends AnyRef

EXPERIMENTAL

This trait defines symbols and operations on them.

Symbols are used to establish bindings between a name and the entity it refers to, such as a class or a method. Anything you define and can give a name to in Scala has an associated symbol.

Symbols contain all available information about the declaration of an entity (class/object/trait etc.) or a member (vals/vars/defs etc.), and as such are an integral abstraction central to both runtime reflection and macros.

A symbol can provide a wealth of information ranging from the basic name method available on all symbols to other, more involved, concepts such as getting the baseClasses from ClassSymbol. Other common use cases of symbols include inspecting members' signatures, getting type parameters of a class, getting the parameter type of a method or finding out the type of a field.

Example usage of runtime reflection; getting a method's type signature:

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

scala> class C[T] { def test[U](x: T)(y: U): Int = ??? }
defined class C

scala> val test = typeOf[C[Int]].member(TermName("test")).asMethod
test: reflect.runtime.universe.MethodSymbol = method test

scala> test.info
res0: reflect.runtime.universe.Type = [U](x: T)(y: U)scala.Int

Symbols are organized in a hierarchy. For example, a symbol that represents a parameter of a method is owned by the corresponding method symbol, a method symbol is owned by its enclosing class, a class is owned by a containing package and so on.

Certain types of tree nodes, such as Ident (references to identifiers) and Select (references to members) expose method symbol to obtain the symbol that represents their declaration. During the typechecking phase, the compiler looks up the symbol based on the name and scope and sets the symbol field of tree nodes.

For more information about Symbol usage and attached intricacies, see the Reflection Guide: Symbols

Self Type
Universe
Source
Symbols.scala
Linear Supertypes
AnyRef, Any
Known Subclasses
JavaUniverse, Universe, Universe
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Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Visibility
  1. Public
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Symbols

  1. abstract type ClassSymbol >: Null <: Universe.ClassSymbolApi with Universe.TypeSymbol

    The type of class symbols representing class and trait definitions.

  2. abstract type MethodSymbol >: Null <: Universe.MethodSymbolApi with Universe.TermSymbol

    The type of method symbols representing def declarations.

  3. abstract type ModuleSymbol >: Null <: Universe.ModuleSymbolApi with Universe.TermSymbol

    The type of module symbols representing object declarations.

  4. abstract type Symbol >: Null <: Universe.SymbolApi

    The type of symbols representing declarations.

  5. abstract type TermSymbol >: Null <: Universe.TermSymbolApi with Universe.Symbol

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

  6. abstract type TypeSymbol >: Null <: Universe.TypeSymbolApi with Universe.Symbol

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

  1. abstract val NoSymbol: Universe.Symbol

    A special "missing" symbol.

    A special "missing" symbol. Commonly used in the API to denote a default or empty value.

API

The methods available for each reflection entity, without the implementation. Since the reflection entities are later overridden by runtime reflection and macros, their API counterparts guarantee a minimum set of methods that are implemented.

  1. trait ClassSymbolApi extends Universe.TypeSymbolApi

    The API of class symbols.

    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.

  2. trait MethodSymbolApi extends Universe.TermSymbolApi

    The API of method symbols.

    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.

  3. trait ModuleSymbolApi extends Universe.TermSymbolApi

    The API of module symbols.

    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.

  4. trait SymbolApi extends AnyRef

    The API of symbols.

    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.

  5. trait TermSymbolApi extends Universe.SymbolApi

    The API of term symbols.

    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.

  6. trait TypeSymbolApi extends Universe.SymbolApi

    The API of type symbols.

    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.