trait Types extends AnyRef
EXPERIMENTAL
A trait that defines types and operations on them.
Type instances represent information about the type of a corresponding symbol. This includes its members (methods, fields, type parameters, nested classes, traits, etc.) either declared directly or inherited, its base types, its erasure and so on. Types also provide operations to test for type conformance or equivalence or for widening.
To instantiate a type, most of the time, the scala.reflect.api.TypeTags#typeOf method can be used. It takes
a type argument and produces a Type
instance which represents that argument. For example:
scala> typeOf[List[Int]] res0: reflect.runtime.universe.Type = scala.List[Int]
In this example, a scala.reflect.api.Types#TypeRef is returned, which corresponds to the type constructor List
applied to the type argument Int
.
Note: Method typeOf
does not work for types with type parameters, such as typeOf[List[A]]
where A
is
a type parameter. In this case, use scala.reflect.api.TypeTags#weakTypeOf instead.
For other ways to instantiate types, see the corresponding section of the Reflection Guide.
Common Operations on Types
Types are typically used for type conformance tests or are queried for declarations of members or inner types.
- Subtyping Relationships can be tested using
<:<
andweak_<:<
. - Type Equality can be checked with
=:=
. It's important to note that==
should not be used to compare types for equality--==
can't check for type equality in the presence of type aliases, while=:=
can.
Types can be queried for members and declarations by using the members
and declarations
methods (along with
their singular counterparts member
and declaration
), which provide the list of definitions associated with that type.
For example, to look up the map
method of List
, one can do:
scala> typeOf[List[_]].member("map": TermName) res1: reflect.runtime.universe.Symbol = method map
For more information about Type
s, see the Reflection Guide: Symbols, Trees, and Types
- Self Type
- Universe
- Source
- Types.scala
- Grouped
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- Types
- AnyRef
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- by any2stringadd
- by StringFormat
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Type Members
-
abstract
type
AnnotatedType
>: Null <: Universe.AnnotatedTypeApi with Universe.Type
The
AnnotatedType
type signature is used for annotated types of the for<type> @<annotation>
. -
trait
AnnotatedTypeApi
extends Universe.TypeApi
The API that all annotated types support.
The API that all annotated types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
AnnotatedTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
AnnotatedType(annotations, underlying)
.An extractor class to create and pattern match with syntax
AnnotatedType(annotations, underlying)
. Here,annotations
are the annotations decorating the underlying typeunderlying
.selfSym
is a symbol representing the annotated type itself. -
abstract
type
BoundedWildcardType
>: Null <: Universe.BoundedWildcardTypeApi with Universe.Type
BoundedWildcardTypes, used only during type inference, are created in two places:
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.
-
trait
BoundedWildcardTypeApi
extends Universe.TypeApi
The API that all this types support.
The API that all this types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
BoundedWildcardTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
BoundedWildcardTypeExtractor(bounds)
withbounds
denoting the type bounds. -
abstract
type
ClassInfoType
>: Null <: Universe.ClassInfoTypeApi with Universe.CompoundType
The
ClassInfo
type signature is used to define parents and declarations of classes, traits, and objects.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 thisC 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)
-
trait
ClassInfoTypeApi
extends Universe.TypeApi
The API that all class info types support.
The API that all class info types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
ClassInfoTypeExtractor
extends AnyRef
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, andclazz
is the symbol of the class itself. -
abstract
type
CompoundType
>: Null <: Universe.CompoundTypeApi with Universe.Type
A subtype of Type representing refined types as well as
ClassInfo
signatures. -
trait
CompoundTypeApi
extends AnyRef
Has no special methods.
Has no special methods. Is here to provides erased identity for
CompoundType
. -
abstract
type
ConstantType
>: Null <: Universe.ConstantTypeApi with Universe.SingletonType
The
ConstantType
type is not directly written in user programs, but arises as the type of a constant.The
ConstantType
type is not directly written in user programs, but arises as the type of a constant. The REPL expresses constant types likeInt(11)
. Here are some constants with their types:1 ConstantType(Constant(1)) "abc" ConstantType(Constant("abc"))
-
trait
ConstantTypeApi
extends Universe.TypeApi
The API that all constant types support.
The API that all constant types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
ConstantTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
ConstantType(constant)
Here,constant
is the constant value represented by the type. -
abstract
type
ExistentialType
>: Null <: Universe.ExistentialTypeApi with Universe.Type
The
ExistentialType
type signature is used for existential types and wildcard types. -
trait
ExistentialTypeApi
extends Universe.TypeApi
The API that all existential types support.
The API that all existential types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
ExistentialTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
ExistentialType(quantified, underlying)
.An extractor class to create and pattern match with syntax
ExistentialType(quantified, underlying)
. Here,quantified
are the type variables bound by the existential type andunderlying
is the type that's existentially quantified. -
abstract
type
MethodType
>: Null <: Universe.MethodTypeApi with Universe.Type
The
MethodType
type signature is used to indicate parameters and result type of a method -
trait
MethodTypeApi
extends Universe.TypeApi
The API that all method types support.
The API that all method types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
MethodTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
MethodType(params, respte)
Here,params
is a potentially empty list of parameter symbols of the method, andrestpe
is the result type of the method.An extractor class to create and pattern match with syntax
MethodType(params, respte)
Here,params
is a potentially empty list of parameter symbols of the method, andrestpe
is the result type of the method. If the method is curried,restpe
would be anotherMethodType
. 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
. -
abstract
type
NullaryMethodType
>: Null <: Universe.NullaryMethodTypeApi with Universe.Type
The
NullaryMethodType
type signature is used for parameterless methods with declarations of the formdef foo: T
-
trait
NullaryMethodTypeApi
extends Universe.TypeApi
The API that all nullary method types support.
The API that all nullary method types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
NullaryMethodTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
NullaryMethodType(resultType)
.An extractor class to create and pattern match with syntax
NullaryMethodType(resultType)
. Here,resultType
is the result type of the parameterless method. -
abstract
type
PolyType
>: Null <: Universe.PolyTypeApi with Universe.Type
The
PolyType
type signature is used for polymorphic methods that have at least one type parameter. -
trait
PolyTypeApi
extends Universe.TypeApi
The API that all polymorphic types support.
The API that all polymorphic types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
PolyTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
PolyType(typeParams, resultType)
.An extractor class to create and pattern match with syntax
PolyType(typeParams, resultType)
. Here,typeParams
are the type parameters of the method andresultType
is the type signature following the type parameters. -
abstract
type
RefinedType
>: Null <: Universe.RefinedTypeApi with Universe.CompoundType
The
RefinedType
type defines types of any of the forms on the left, with their RefinedType representations to the right.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))
-
trait
RefinedTypeApi
extends Universe.TypeApi
The API that all refined types support.
The API that all refined types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
RefinedTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
RefinedType(parents, decls)
Here,parents
is the list of parent types of the class, anddecls
is the scope containing all declarations in the class. -
abstract
type
SingleType
>: Null <: Universe.SingleTypeApi with Universe.SingletonType
The
SingleType
type describes types of any of the forms on the left, with their TypeRef representations to the right.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)
-
trait
SingleTypeApi
extends Universe.TypeApi
The API that all single types support.
The API that all single types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
SingleTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
SingleType(pre, sym)
Here,pre
is the prefix of the single-type, andsym
is the stable value symbol referred to by the single-type. -
abstract
type
SingletonType
>: Null <: Universe.SingletonTypeApi with Universe.Type
The type of Scala singleton types, i.e., types that are inhabited by only one nun-null value.
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.
-
trait
SingletonTypeApi
extends AnyRef
Has no special methods.
Has no special methods. Is here to provides erased identity for
SingletonType
. -
abstract
type
SuperType
>: Null <: Universe.SuperTypeApi with Universe.SingletonType
The
SuperType
type is not directly written, but arises whenC.super
is used as a prefix in aTypeRef
orSingleType
.The
SuperType
type is not directly written, but arises whenC.super
is used as a prefix in aTypeRef
orSingleType
. It's internal presentation isSuperType(thistpe, supertpe)
Here,
thistpe
is the type of the corresponding this-type. For instance, in the type arising from C.super, thethistpe
part would beThisType(C)
.supertpe
is the type of the super class referred to by thesuper
. -
trait
SuperTypeApi
extends Universe.TypeApi
The API that all super types support.
The API that all super types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
SuperTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
SingleType(thistpe, supertpe)
-
abstract
type
ThisType
>: Null <: Universe.ThisTypeApi with Universe.SingletonType
A singleton type that describes types of the form on the left with the corresponding
ThisType
representation to the right: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)
-
trait
ThisTypeApi
extends Universe.TypeApi
The API that all this types support.
The API that all this types support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
ThisTypeExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
ThisType(sym)
wheresym
is the class prefix of the this type. -
abstract
type
Type
>: Null <: Universe.TypeApi
The type of Scala types, and also Scala type signatures.
The type of Scala types, and also Scala type signatures. (No difference is internally made between the two).
-
abstract
class
TypeApi
extends AnyRef
The API of types.
The API of types. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
type
TypeBounds
>: Null <: Universe.TypeBoundsApi with Universe.Type
The
TypeBounds
type signature is used to indicate lower and upper type bounds of type parameters and abstract types.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)
-
trait
TypeBoundsApi
extends Universe.TypeApi
The API that all type bounds support.
The API that all type bounds support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
TypeBoundsExtractor
extends AnyRef
An extractor class to create and pattern match with syntax
TypeBound(lower, upper)
Here,lower
is the lower bound of theTypeBounds
pair, andupper
is the upper bound. -
abstract
type
TypeRef
>: Null <: Universe.TypeRefApi with Universe.Type
The
TypeRef
type describes types of any of the forms on the left, with their TypeRef representations to the right.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)
-
trait
TypeRefApi
extends Universe.TypeApi
The API that all type refs support.
The API that all type refs support. The main source of information about types is the scala.reflect.api.Types page.
-
abstract
class
TypeRefExtractor
extends AnyRef
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, andargs
is a possible empty list of type arguments.
Abstract Value Members
-
abstract
val
AnnotatedType: Universe.AnnotatedTypeExtractor
The constructor/extractor for
AnnotatedType
instances. -
abstract
val
BoundedWildcardType: Universe.BoundedWildcardTypeExtractor
The constructor/extractor for
BoundedWildcardType
instances. -
abstract
val
ClassInfoType: Universe.ClassInfoTypeExtractor
The constructor/extractor for
ClassInfoType
instances. -
abstract
val
ConstantType: Universe.ConstantTypeExtractor
The constructor/extractor for
ConstantType
instances. -
abstract
val
ExistentialType: Universe.ExistentialTypeExtractor
The constructor/extractor for
ExistentialType
instances. -
abstract
val
MethodType: Universe.MethodTypeExtractor
The constructor/extractor for
MethodType
instances. -
abstract
val
NoPrefix: Universe.Type
This constant is used as a special value denoting the empty prefix in a path dependent type.
This constant is used as a special value denoting the empty prefix in a path dependent type. For instance
x.type
is represented asSingleType(NoPrefix, <x>)
, where<x>
stands for the symbol forx
. -
abstract
val
NoType: Universe.Type
This constant is used as a special value that indicates that no meaningful type exists.
-
abstract
val
NullaryMethodType: Universe.NullaryMethodTypeExtractor
The constructor/extractor for
NullaryMethodType
instances. -
abstract
val
PolyType: Universe.PolyTypeExtractor
The constructor/extractor for
PolyType
instances. -
abstract
val
RefinedType: Universe.RefinedTypeExtractor
The constructor/extractor for
RefinedType
instances. -
abstract
val
SingleType: Universe.SingleTypeExtractor
The constructor/extractor for
SingleType
instances. -
abstract
val
SuperType: Universe.SuperTypeExtractor
The constructor/extractor for
SuperType
instances. -
abstract
val
ThisType: Universe.ThisTypeExtractor
The constructor/extractor for
ThisType
instances. -
abstract
val
TypeBounds: Universe.TypeBoundsExtractor
The constructor/extractor for
TypeBounds
instances. -
abstract
val
TypeRef: Universe.TypeRefExtractor
The constructor/extractor for
TypeRef
instances. -
abstract
val
WildcardType: Universe.Type
An object representing an unknown type, used during type inference.
An object representing an unknown type, used during type inference. If you see WildcardType outside of inference it is almost certainly a bug.
-
abstract
def
appliedType(sym: Universe.Symbol, args: Universe.Type*): Universe.Type
- See also
-
abstract
def
appliedType(sym: Universe.Symbol, args: List[Universe.Type]): Universe.Type
- See also
-
abstract
def
appliedType(tycon: Universe.Type, args: Universe.Type*): Universe.Type
- See also
-
abstract
def
appliedType(tycon: Universe.Type, args: List[Universe.Type]): Universe.Type
A creator for type applications
-
abstract
def
glb(ts: List[Universe.Type]): Universe.Type
The greatest lower bound of a list of types, as determined by
<:<
. -
abstract
def
lub(xs: List[Universe.Type]): Universe.Type
The least upper bound of a list of types, as determined by
<:<
.
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): (Types, 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: (Types) ⇒ Boolean, msg: ⇒ Any): Types
- def ensuring(cond: (Types) ⇒ Boolean): Types
- def ensuring(cond: Boolean, msg: ⇒ Any): Types
- def ensuring(cond: Boolean): Types
-
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): (Types, B)
Types - Operations
Types
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.
Extractors
Extractors provide the machinery necessary to allow pattern matching and construction of reflection entities that is similar to case classes, although the entities are only abstract types that are later overridden.