scala.reflect

ClassTag

Related Docs: object ClassTag | package reflect

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 Arrays whose element types are unknown at compile time.

ClassTags 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, ClassTags 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
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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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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

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    AnyRef → Any
  2. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types and null.

    Equivalent to x.hashCode except for boxed numeric types and null. 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. For null returns a hashcode where null.hashCode throws a NullPointerException.

    returns

    a hash value consistent with ==

    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

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    arg0

    the object to compare against this object for equality.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    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

    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 a ClassCastException at runtime, while the expression List(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 type T0.

  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
    ClassTagEqualsClassManifestDeprecatedApis
  10. 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

  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

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    • It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
    • For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
    • null.eq(null) returns true.

    When overriding the equals or hashCode 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
  16. def equals(x: Any): Boolean

    The universal equality method defined in AnyRef.

    The universal equality method defined in AnyRef.

    Definition Classes
    ClassTagEquals → AnyRef → Any
  17. 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 between finalize 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

  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[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

    a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
    AnyRef → Any
    Note

    not specified by SLS as a member of AnyRef

  20. def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in scala.Any.

    returns

    the hash code value for this object.

    Definition Classes
    ClassTag → AnyRef → Any
  21. 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 return false, while the expression List(1).isInstanceOf[List[String]] will return true. 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 type T0; false otherwise.

    Definition Classes
    Any
  22. 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
  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
    ClassTagClassManifestDeprecatedApis
  24. 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

  25. 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

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

    Definition Classes
    AnyRef
  27. 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
    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