scala.reflect

# ClassTag

#### trait ClassTag[T] extends ClassManifestDeprecatedApis[T] with Equals with Serializable

A `ClassTag[T]` stores the erased class of a given type `T`, accessible via the `runtimeClass` field. This is particularly useful for instantiating `Array`s whose element types are unknown at compile time.

`ClassTag`s are a weaker special case of scala.reflect.api.TypeTags#TypeTags, in that they wrap only the runtime class of a given type, whereas a `TypeTag` contains all static type information. That is, `ClassTag`s are constructed from knowing only the top-level class of a type, without necessarily knowing all of its argument types. This runtime information is enough for runtime `Array` creation.

For example:

    scala> def mkArray[T : ClassTag](elems: T*) = Array[T](elems: _*)
    mkArray: [T](elems: T*)(implicit evidence$1: scala.reflect.ClassTag[T])Array[T]

    scala> mkArray(42, 13)
    res0: Array[Int] = Array(42, 13)

    scala> mkArray("Japan","Brazil","Germany")
    res1: Array[String] = Array(Japan, Brazil, Germany)

See scala.reflect.api.TypeTags for more examples, or the Reflection Guide: TypeTags for more details.

Annotations
  @implicitNotFound( msg = "No ClassTag available for ${T}" )
Source
  ClassTag.scala

Linear Supertypes
Equals, ClassManifestDeprecatedApis[T], OptManifest[T], Serializable, java.io.Serializable, AnyRef, Any
Known Subclasses
AnyValManifest, Manifest
Type Hierarchy Learn more about scaladoc diagrams
Ordering

1. Alphabetic
2. By inheritance

Inherited

1. ClassTag
2. Equals
3. ClassManifestDeprecatedApis
4. OptManifest
5. Serializable
6. Serializable
7. AnyRef
8. Any

Implicitly

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

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Visibility

1. Public
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### Abstract Value Members

1. #### abstract def runtimeClass: Class[_]

   A class representing the type `U` to which `T` would be erased.

   A class representing the type `U` to which `T` would be erased. Note that there is no subtyping relationship between `T` and `U`.

### 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 ClassTag[T] to any2stringadd[ClassTag[T]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd

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

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

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

   Definition Classes
     AnyRef → Any

6. #### def argString: String

   Attributes
     protected
   Definition Classes
     ClassManifestDeprecatedApis

7. #### def arrayClass[T](tp: Class[_]): Class[Array[T]]

   Attributes
     protected
   Definition Classes
     ClassManifestDeprecatedApis

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

   Definition Classes
     Any

9. #### def canEqual(x: Any): Boolean

   A method that should be called from every well-designed equals method that is open to be overridden in a subclass.

   A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

   returns

     true if this instance can possibly equal `that`, otherwise false

   Definition Classes
     ClassTag → Equals → ClassManifestDeprecatedApis

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

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

11. #### def ensuring(cond: (ClassTag[T]) ⇒ Boolean, msg: ⇒ Any): ClassTag[T]

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

12. #### def ensuring(cond: (ClassTag[T]) ⇒ Boolean): ClassTag[T]

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

13. #### def ensuring(cond: Boolean, msg: ⇒ Any): ClassTag[T]

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

14. #### def ensuring(cond: Boolean): ClassTag[T]

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

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

    Definition Classes
      AnyRef

16. #### def equals(x: Any): Boolean

    The universal equality method defined in `AnyRef`.

    The universal equality method defined in `AnyRef`.

    Definition Classes
      ClassTag → Equals → AnyRef → Any

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

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

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

    Returns string formatted according to given `format` string.

    Returns string formatted according to given `format` string. Format strings are as for `String.format` (@see java.lang.String.format).

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

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

    Definition Classes
      AnyRef → Any

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

    Definition Classes
      ClassTag → AnyRef → Any

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

    Definition Classes
      Any

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

    Definition Classes
      AnyRef

23. #### def newArray(len: Int): Array[T]

    Produces a new array with element type `T` and length `len`

    Produces a new array with element type `T` and length `len`

    Definition Classes
      ClassTag → ClassManifestDeprecatedApis

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

    Definition Classes
      AnyRef

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

    Definition Classes
      AnyRef

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

    Definition Classes
      AnyRef

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

    Definition Classes
      ClassTag → AnyRef → Any

28. #### def unapply(x: Unit): Option[T]

29. #### def unapply(x: Boolean): Option[T]

30. #### def unapply(x: Double): Option[T]

31. #### def unapply(x: Float): Option[T]

32. #### def unapply(x: Long): Option[T]

33. #### def unapply(x: Int): Option[T]

34. #### def unapply(x: Char): Option[T]

35. #### def unapply(x: Short): Option[T]

36. #### def unapply(x: Byte): Option[T]

37. #### def unapply(x: Any): Option[T]

    A ClassTag[T] can serve as an extractor that matches only objects of type T.

    A ClassTag[T] can serve as an extractor that matches only objects of type T.

    The compiler tries to turn unchecked type tests in pattern matches into checked ones by wrapping a `(_: T)` type pattern as `ct(_: T)`, where `ct` is the `ClassTag[T]` instance. Type tests necessary before calling other extractors are treated similarly. `SomeExtractor(...)` is turned into `ct(SomeExtractor(...))` if `T` in `SomeExtractor.unapply(x: T)` is uncheckable, but we have an instance of `ClassTag[T]`.

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

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

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

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

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

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

41. #### def wrap: ClassTag[Array[T]]

    Produces a `ClassTag` that knows how to instantiate an `Array[Array[T]]`

42. #### def →[B](y: B): (ClassTag[T], B)

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

### Deprecated Value Members

1. #### def <:<(that: ClassManifest[_]): Boolean

   Tests whether the type represented by this manifest is a subtype of the type represented by `that` manifest, subject to the limitations described in the header.

   Tests whether the type represented by this manifest is a subtype of the type represented by `that` manifest, subject to the limitations described in the header.

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use scala.reflect.runtime.universe.TypeTag for subtype checking instead

2. #### def >:>(that: ClassManifest[_]): Boolean

   Tests whether the type represented by this manifest is a supertype of the type represented by `that` manifest, subject to the limitations described in the header.

   Tests whether the type represented by this manifest is a supertype of the type represented by `that` manifest, subject to the limitations described in the header.

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use scala.reflect.runtime.universe.TypeTag for subtype checking instead

3. #### def arrayManifest: ClassManifest[Array[T]]

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use wrap instead

4. #### def erasure: Class[_]

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use runtimeClass instead

5. #### def newArray2(len: Int): Array[Array[T]]

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use wrap.newArray instead

6. #### def newArray3(len: Int): Array[Array[Array[T]]]

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use wrap.wrap.newArray instead

7. #### def newArray4(len: Int): Array[Array[Array[Array[T]]]]

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use wrap.wrap.wrap.newArray instead

8. #### def newArray5(len: Int): Array[Array[Array[Array[Array[T]]]]]

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use wrap.wrap.wrap.wrap.newArray instead

9. #### def newArrayBuilder(): ArrayBuilder[T]

   Definition Classes
     ClassManifestDeprecatedApis
   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use ArrayBuilder.make(this) instead

10. #### def newWrappedArray(len: Int): WrappedArray[T]

    Definition Classes
      ClassManifestDeprecatedApis
    Annotations
      @deprecated
    Deprecated

      (Since version 2.10.0) Create WrappedArray directly instead

11. #### def typeArguments: List[OptManifest[_]]

    Definition Classes
      ClassManifestDeprecatedApis
    Annotations
      @deprecated
    Deprecated

      (Since version 2.10.0) Use scala.reflect.runtime.universe.TypeTag to capture type structure instead

### Inherited from Equals

### Inherited from ClassManifestDeprecatedApis[T]

### Inherited from OptManifest[T]

### Inherited from Serializable

### Inherited from java.io.Serializable

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from ClassTag[T] to any2stringadd[ClassTag[T]]

### Inherited by implicit conversion StringFormat from ClassTag[T] to StringFormat[ClassTag[T]]

### Inherited by implicit conversion Ensuring from ClassTag[T] to Ensuring[ClassTag[T]]

### Inherited by implicit conversion ArrowAssoc from ClassTag[T] to ArrowAssoc[ClassTag[T]]

### Ungrouped