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
- Grouped
- Alphabetic
- By Inheritance
- Symbols
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
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- Public
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Type Members
-
abstract
type
ClassSymbol
>: Null <: Universe.ClassSymbolApi with Universe.TypeSymbol
The type of class symbols representing class and trait definitions.
-
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 asisPublic
orisFinal
,params
andreturnType
methods for method symbols,baseClasses
for class symbols and so on. Some of these methods don't make sense for certain subclasses ofSymbol
and returnNoSymbol
,Nil
or other empty values. -
abstract
type
MethodSymbol
>: Null <: Universe.MethodSymbolApi with Universe.TermSymbol
The type of method symbols representing def declarations.
-
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 asisPublic
orisFinal
,params
andreturnType
methods for method symbols,baseClasses
for class symbols and so on. Some of these methods don't make sense for certain subclasses ofSymbol
and returnNoSymbol
,Nil
or other empty values. -
abstract
type
ModuleSymbol
>: Null <: Universe.ModuleSymbolApi with Universe.TermSymbol
The type of module symbols representing object declarations.
-
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 asisPublic
orisFinal
,params
andreturnType
methods for method symbols,baseClasses
for class symbols and so on. Some of these methods don't make sense for certain subclasses ofSymbol
and returnNoSymbol
,Nil
or other empty values. -
abstract
type
Symbol
>: Null <: Universe.SymbolApi
The type of symbols representing declarations.
-
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 asisPublic
orisFinal
,params
andreturnType
methods for method symbols,baseClasses
for class symbols and so on. Some of these methods don't make sense for certain subclasses ofSymbol
and returnNoSymbol
,Nil
or other empty values. -
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.
-
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 asisPublic
orisFinal
,params
andreturnType
methods for method symbols,baseClasses
for class symbols and so on. Some of these methods don't make sense for certain subclasses ofSymbol
and returnNoSymbol
,Nil
or other empty values. -
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.
-
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 asisPublic
orisFinal
,params
andreturnType
methods for method symbols,baseClasses
for class symbols and so on. Some of these methods don't make sense for certain subclasses ofSymbol
and returnNoSymbol
,Nil
or other empty values.
Abstract Value Members
-
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.
Concrete Value Members
-
final
def
!=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
- returns
true
if !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
-
final
def
##(): Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
- def +(other: String): String
- def ->[B](y: B): (Symbols, B)
-
final
def
==(arg0: Any): Boolean
The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.- returns
true
if the receiver object is equivalent to the argument;false
otherwise.
- Definition Classes
- AnyRef → Any
-
final
def
asInstanceOf[T0]: T0
Cast the receiver object to be of type
T0
.Cast the receiver object to be of type
T0
.Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression
1.asInstanceOf[String]
will throw aClassCastException
at runtime, while the expressionList(1).asInstanceOf[List[String]]
will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastException
if the receiver object is not an instance of the erasure of typeT0
.
-
def
clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the
clone
method is platform dependent.- returns
a copy of the receiver object.
- Attributes
- protected[java.lang]
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
- Note
not specified by SLS as a member of AnyRef
- def ensuring(cond: (Symbols) ⇒ Boolean, msg: ⇒ Any): Symbols
- def ensuring(cond: (Symbols) ⇒ Boolean): Symbols
- def ensuring(cond: Boolean, msg: ⇒ Any): Symbols
- def ensuring(cond: Boolean): Symbols
-
final
def
eq(arg0: AnyRef): Boolean
Tests whether the argument (
that
) is a reference to the receiver object (this
).Tests whether the argument (
that
) is a reference to the receiver object (this
).The
eq
method implements an equivalence relation on non-null instances ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2
), they should be equal to each other (o1 == o2
) and they should hash to the same value (o1.hashCode == o2.hashCode
).- returns
true
if the argument is a reference to the receiver object;false
otherwise.
- Definition Classes
- AnyRef
- It is consistent: for any non-null instances
-
def
equals(arg0: Any): Boolean
The equality method for reference types.
-
def
finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the
finalize
method is invoked, as well as the interaction betweenfinalize
and non-local returns and exceptions, are all platform dependent.- Attributes
- protected[java.lang]
- Definition Classes
- AnyRef
- Annotations
- @throws( classOf[java.lang.Throwable] )
- Note
not specified by SLS as a member of AnyRef
- def formatted(fmtstr: String): String
-
final
def
getClass(): Class[_]
Returns the runtime class representation of the object.
Returns the runtime class representation of the object.
- returns
a class object corresponding to the runtime type of the receiver.
- Definition Classes
- AnyRef → Any
-
def
hashCode(): Int
The hashCode method for reference types.
-
final
def
isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object is
T0
.Test whether the dynamic type of the receiver object is
T0
.Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression
1.isInstanceOf[String]
will returnfalse
, while the expressionList(1).isInstanceOf[List[String]]
will returntrue
. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.- returns
true
if the receiver object is an instance of erasure of typeT0
;false
otherwise.
- Definition Classes
- Any
-
final
def
ne(arg0: AnyRef): Boolean
Equivalent to
!(this eq that)
.Equivalent to
!(this eq that)
.- returns
true
if the argument is not a reference to the receiver object;false
otherwise.
- Definition Classes
- AnyRef
-
final
def
notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Note
not specified by SLS as a member of AnyRef
-
final
def
notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Note
not specified by SLS as a member of AnyRef
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
-
def
toString(): String
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
- returns
a String representation of the object.
- Definition Classes
- AnyRef → Any
-
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( ... )
- def →[B](y: B): (Symbols, B)
Symbols
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.