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/Scala 2.13 Reflection

Trait scala.reflect.api.Types

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.

In the case of a generic type, you can also combine it with other types using scala.reflect.api.Types#appliedType. For example:

scala> val intType = typeOf[Int]
intType: reflect.runtime.universe.Type = Int

scala> val listType = typeOf[List[_]]
listType: reflect.runtime.universe.Type = List[_]

scala> appliedType(listType.typeConstructor, intType)
res0: reflect.runtime.universe.Type = List[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 <:< and weak_<:<.
  • 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(TermName("map"))
res1: reflect.runtime.universe.Symbol = method map

For more information about Types, see the Reflection Guide: Symbols, Trees, and Types

Self Type
Universe
Source
Types.scala
Linear Supertypes
AnyRef, Any
Known Subclasses
JavaUniverse, Universe, Universe

Type Members

abstract type AnnotatedType >: Null <: Universe.AnnotatedTypeApi with Universe.Type

trait AnnotatedTypeApi extends Universe.TypeApi

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). Here, annotations are the annotations decorating the underlying type underlying. 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:

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

abstract class BoundedWildcardTypeExtractor extends AnyRef

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. 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)

trait ClassInfoTypeApi extends Universe.TypeApi

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

abstract type CompoundType >: Null <: Universe.CompoundTypeApi with Universe.Type

trait CompoundTypeApi extends AnyRef

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

abstract type ConstantType >: Null <: Universe.ConstantTypeApi with Universe.SingletonType

A ConstantType type cannot be expressed in user programs; it is inferred as the type of a constant. Here are some constants with their types and the internal string representation:

1           ConstantType(Constant(1))       Int(1)
"abc"       ConstantType(Constant("abc"))   String("abc")

ConstantTypes denote values that may safely be constant folded during type checking. The deconst operation returns the equivalent type that will not be constant folded.

trait ConstantTypeApi extends Universe.TypeApi

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

abstract type ExistentialType >: Null <: Universe.ExistentialTypeApi with Universe.Type

trait ExistentialTypeApi extends Universe.TypeApi

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). Here, quantified are the type variables bound by the existential type and underlying is the type that's existentially quantified.

abstract type MethodType >: Null <: Universe.MethodTypeApi with Universe.Type

trait MethodTypeApi extends Universe.TypeApi

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, 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.

abstract type NullaryMethodType >: Null <: Universe.NullaryMethodTypeApi with Universe.Type

trait NullaryMethodTypeApi extends Universe.TypeApi

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). Here, resultType is the result type of the parameterless method.

abstract type PolyType >: Null <: Universe.PolyTypeApi with Universe.Type

trait PolyTypeApi extends Universe.TypeApi

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). Here, typeParams are the type parameters of the method and resultType 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.

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

abstract class RefinedTypeExtractor extends AnyRef

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.

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

abstract class SingleTypeExtractor extends AnyRef

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. 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. 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 when C.super is used as a prefix in a TypeRef or SingleType. Its 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.

trait SuperTypeApi extends Universe.TypeApi

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

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:

C.this.type             ThisType(C)

trait ThisTypeApi extends Universe.TypeApi

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

abstract type Type >: Null <: Universe.TypeApi

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

abstract class TypeBoundsExtractor extends AnyRef

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.

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

abstract class TypeRefExtractor extends AnyRef

Abstract Value Members

abstract val AnnotatedType: Universe.AnnotatedTypeExtractor

abstract val BoundedWildcardType: Universe.BoundedWildcardTypeExtractor

abstract val ClassInfoType: Universe.ClassInfoTypeExtractor

abstract val ConstantType: Universe.ConstantTypeExtractor

abstract val ExistentialType: Universe.ExistentialTypeExtractor

abstract val MethodType: Universe.MethodTypeExtractor

abstract val NoPrefix: Universe.Type

This constant is used as a special value denoting the empty prefix in a path dependent type. For instance x.type is represented as SingleType(NoPrefix, <x>), where <x> stands for the symbol for x.

abstract val NoType: Universe.Type

abstract val NullaryMethodType: Universe.NullaryMethodTypeExtractor

abstract val PolyType: Universe.PolyTypeExtractor

abstract val RefinedType: Universe.RefinedTypeExtractor

abstract val SingleType: Universe.SingleTypeExtractor

abstract val SuperType: Universe.SuperTypeExtractor

abstract val ThisType: Universe.ThisTypeExtractor

abstract val TypeBounds: Universe.TypeBoundsExtractor

abstract val TypeRef: Universe.TypeRefExtractor

abstract val WildcardType: Universe.Type

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

appliedType

abstract def appliedType(sym: Universe.Symbol, args: List[Universe.Type]): Universe.Type

See also

appliedType

abstract def appliedType(tycon: Universe.Type, args: Universe.Type*): Universe.Type

See also

appliedType

abstract def appliedType(tycon: Universe.Type, args: List[Universe.Type]): Universe.Type

A creator for type applications.

Useful to combine and create types out of generic ones. For example:

scala> val boolType = typeOf[Boolean]
boolType: reflect.runtime.universe.Type = Boolean

scala> val optionType = typeOf[Option[_]]
optionType: reflect.runtime.universe.Type = Option[_]

scala> appliedType(optionType.typeConstructor, boolType)
res0: reflect.runtime.universe.Type = Option[Boolean]

abstract def glb(ts: List[Universe.Type]): Universe.Type

abstract def lub(xs: List[Universe.Type]): Universe.Type

Concrete Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any

final def ##(): Int

Definition Classes
AnyRef → Any

def +(other: String): String

Implicit
This member is added by an implicit conversion from Types toany2stringadd[Types] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

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

Implicit
This member is added by an implicit conversion from Types toArrowAssoc[Types] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()

final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any

final def asInstanceOf[T0]: T0

Definition Classes
Any

def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()

def ensuring(cond: (Types) => Boolean, msg: => Any): Types

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

def ensuring(cond: (Types) => Boolean): Types

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

def ensuring(cond: Boolean, msg: => Any): Types

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

def ensuring(cond: Boolean): Types

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

final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef

def equals(arg0: AnyRef): Boolean

Definition Classes
AnyRef → Any

def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])

def formatted(fmtstr: String): String

Implicit
This member is added by an implicit conversion from Types toStringFormat[Types] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()

final def getClass(): Class[_ <: AnyRef]

Definition Classes
AnyRef → Any
Annotations
@native()

def hashCode(): Int

Definition Classes
AnyRef → Any
Annotations
@native()

final def isInstanceOf[T0]: Boolean

Definition Classes
Any

final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef

final def notify(): Unit

Definition Classes
AnyRef
Annotations
@native()

final def notifyAll(): Unit

Definition Classes
AnyRef
Annotations
@native()

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def toString(): String

Definition Classes
AnyRef → Any

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

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

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala-reflect/scala/reflect/api/Types.html