scala.reflect.api

# TypeTags

#### trait TypeTags extends AnyRef

A `TypeTag[T]` encapsulates the runtime type representation of some type `T`. Like scala.reflect.Manifest, the prime use case of `TypeTag`s is to give access to erased types. However, `TypeTag`s should be considered to be a richer replacement of the pre-2.10 notion of a Manifest, that are, in addition, fully integrated with Scala reflection.

There exist three different types of `TypeTags`:

- scala.reflect.api.TypeTags#TypeTag.
  A full type descriptor of a Scala type. For example, a `TypeTag[List[String]]` contains all type information, in this case, of type `scala.List[String]`.
- scala.reflect.ClassTag.
  A partial type descriptor of a Scala type. For example, a `ClassTag[List[String]]` contains only the erased class type information, in this case, of type `scala.collection.immutable.List`. `ClassTag`s provide access only to the runtime class of a type. Analogous to scala.reflect.ClassManifest
- scala.reflect.api.TypeTags#WeakTypeTag.
  A type descriptor for abstract types (see description below).

Like Manifests, `TypeTag`s are always generated by the compiler, and can be obtained in three ways:

##### #1 Via the methods typeTag, classTag, or weakTypeTag

For example:

    import scala.reflect.runtime.universe._
    val tt = typeTag[Int]

    import scala.reflect._
    val ct = classTag[String]

Each of these methods constructs a `TypeTag[T]` or `ClassTag[T]` for the given type argument `T`.

##### #2 Using an implicit parameter of type `TypeTag[T]`, `ClassTag[T]`, or `WeakTypeTag[T]`

For example:

    import scala.reflect.runtime.universe._

    def paramInfo[T](x: T)(implicit tag: TypeTag[T]): Unit = {
      val targs = tag.tpe match { case TypeRef(_, _, args) => args }
      println(s"type of $x has type arguments $targs")
    }

    scala> paramInfo(42)
    type of 42 has type arguments List()

    scala> paramInfo(List(1, 2))
    type of List(1, 2) has type arguments List(Int)

##### #3 Context bound of a type parameter

...on methods or classes. The above example can be implemented as follows:

    import scala.reflect.runtime.universe._

    def paramInfo[T: TypeTag](x: T): Unit = {
      val targs = typeOf[T] match { case TypeRef(_, _, args) => args }
      println(s"type of $x has type arguments $targs")
    }

    scala> paramInfo(42)
    type of 42 has type arguments List()

    scala> paramInfo(List(1, 2))
    type of List(1, 2) has type arguments List(Int)

##### `WeakTypeTag`s

`WeakTypeTag[T]` generalizes `TypeTag[T]`. Unlike a regular `TypeTag`, components of its type representation can be references to type parameters or abstract types. However, `WeakTypeTag[T]` tries to be as concrete as possible, i.e. if type tags are available for the referenced type arguments or abstract types, they are used to embed the concrete types into the `WeakTypeTag[T]`.

Continuing the example above:

    def weakParamInfo[T](x: T)(implicit tag: WeakTypeTag[T]): Unit = {
      val targs = tag.tpe match { case TypeRef(_, _, args) => args }
      println(s"type of $x has type arguments $targs")
    }

    scala> def foo[T] = weakParamInfo(List[T]())
    foo: [T]=> Unit

    scala> foo[Int]
    type of List() has type arguments List(T)

##### TypeTags and Manifests

`TypeTag`s correspond loosely to the pre-2.10 notion of scala.reflect.Manifests. While scala.reflect.ClassTag corresponds to scala.reflect.ClassManifest and scala.reflect.api.TypeTags#TypeTag mostly corresponds to scala.reflect.Manifest, other pre-2.10 `Manifest` types do not have a direct correspondence with a 2.10 "`Tag`" type.

- scala.reflect.OptManifest is not supported.
  This is because `Tag`s can reify arbitrary types, so they are always available. -
- There is no equivalent for scala.reflect.AnyValManifest.
  Instead, one can compare their `Tag` with one of the base `Tag`s (defined in the corresponding companion objects) in order to find out whether or not it represents a primitive value class. Additionally, it's possible to simply use `<tag>.tpe.typeSymbol.isPrimitiveValueClass`.
- There are no replacement for factory methods defined in the `Manifest` companion objects.
  Instead, one could generate corresponding types using the reflection APIs provided by Java (for classes) and Scala (for types).
- Certain manifest operations(i.e., <:<, >:> and typeArguments) are not supported.
  Instead, one could use the reflection APIs provided by Java (for classes) and Scala (for types).

In Scala 2.10, scala.reflect.ClassManifests are deprecated, and it is planned to deprecate scala.reflect.Manifest in favor of `TypeTag`s and `ClassTag`s in an upcoming point release. Thus, it is advisable to migrate any `Manifest`-based APIs to use `Tag`s.

For more information about `TypeTag`s, see the Reflection Guide: TypeTags

Self Type
  Universe
See also

  scala.reflect.ClassTag, scala.reflect.api.TypeTags#TypeTag, scala.reflect.api.TypeTags#WeakTypeTag

Linear Supertypes
AnyRef, Any
Known Subclasses
JavaUniverse, Universe, Universe
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Inherited

1. TypeTags
2. AnyRef
3. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

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### Type Members

1. #### trait TypeTag[T] extends Universe.WeakTypeTag[T] with Equals with Serializable

   A `TypeTag` is a scala.reflect.api.TypeTags#WeakTypeTag with the additional static guarantee that all type references are concrete, i.

2. #### trait WeakTypeTag[T] extends Equals with Serializable

   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.

### Abstract Value Members

1. #### abstract def symbolOf[T](implicit arg0: Universe.WeakTypeTag[T]): Universe.TypeSymbol

   Type symbol of `x` as derived from a type tag.

### Concrete Value Members

1. #### final def !=(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

2. #### final def ##(): Int

   Definition Classes
     AnyRef → Any

3. #### def +(other: String): String

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

4. #### def ->[B](y: B): (TypeTags, B)

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

5. #### final def ==(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

6. #### object TypeTag extends Serializable

   Type tags corresponding to primitive types and constructor/extractor for WeakTypeTags.

7. #### object WeakTypeTag extends Serializable

   Type tags corresponding to primitive types and constructor/extractor for WeakTypeTags.

8. #### final def asInstanceOf[T0]: T0

   Definition Classes
     Any

9. #### def clone(): AnyRef

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

10. #### def ensuring(cond: (TypeTags) ⇒ Boolean, msg: ⇒ Any): TypeTags

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

11. #### def ensuring(cond: (TypeTags) ⇒ Boolean): TypeTags

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

12. #### def ensuring(cond: Boolean, msg: ⇒ Any): TypeTags

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

13. #### def ensuring(cond: Boolean): TypeTags

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

14. #### final def eq(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

15. #### def equals(arg0: Any): Boolean

    Definition Classes
      AnyRef → Any

16. #### def finalize(): Unit

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

17. #### def formatted(fmtstr: String): String

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

18. #### final def getClass(): Class[_]

    Definition Classes
      AnyRef → Any

19. #### def hashCode(): Int

    Definition Classes
      AnyRef → Any

20. #### final def isInstanceOf[T0]: Boolean

    Definition Classes
      Any

21. #### final def ne(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

22. #### final def notify(): Unit

    Definition Classes
      AnyRef

23. #### final def notifyAll(): Unit

    Definition Classes
      AnyRef

24. #### final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
      AnyRef

25. #### def toString(): String

    Definition Classes
      AnyRef → Any

26. #### def typeOf[T](implicit ttag: Universe.TypeTag[T]): Universe.Type

    Shortcut for `implicitly[TypeTag[T]].tpe`

27. #### def typeTag[T](implicit ttag: Universe.TypeTag[T]): Universe.TypeTag[T]

    Shortcut for `implicitly[TypeTag[T]]`

28. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

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

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

30. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

31. #### def weakTypeOf[T](implicit attag: Universe.WeakTypeTag[T]): Universe.Type

    Shortcut for `implicitly[WeakTypeTag[T]].tpe`

32. #### def weakTypeTag[T](implicit attag: Universe.WeakTypeTag[T]): Universe.WeakTypeTag[T]

    Shortcut for `implicitly[WeakTypeTag[T]]`

33. #### def →[B](y: B): (TypeTags, B)

    Implicit information
      This member is added by an implicit conversion from TypeTags to ArrowAssoc[TypeTags] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from TypeTags to any2stringadd[TypeTags]

### Inherited by implicit conversion StringFormat from TypeTags to StringFormat[TypeTags]

### Inherited by implicit conversion Ensuring from TypeTags to Ensuring[TypeTags]

### Inherited by implicit conversion ArrowAssoc from TypeTags to ArrowAssoc[TypeTags]

### TypeTags

### Ungrouped