ClassTag

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}" )

Linear Supertypes

Equals, ClassManifestDeprecatedApis[T], OptManifest[T], Serializable, java.io.Serializable, AnyRef, Any

Known Subclasses

AnyValManifest, Manifest

Abstract Value Members

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

final def !=(arg0: Any): Boolean

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

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
def argString: String

Attributes
protected
Definition Classes
ClassManifestDeprecatedApis
def arrayClass[T](tp: Class[_]): Class[Array[T]]

Attributes
protected
Definition Classes
ClassManifestDeprecatedApis
final def asInstanceOf[T0]: T0

Definition Classes
Any
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
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
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
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def hashCode(): Int

Definition Classes
ClassTag → AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
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
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def toString(): String

Definition Classes
ClassTag → AnyRef → Any
def unapply(x: Unit): Option[T]
def unapply(x: Boolean): Option[T]
def unapply(x: Double): Option[T]
def unapply(x: Float): Option[T]
def unapply(x: Long): Option[T]
def unapply(x: Int): Option[T]
def unapply(x: Char): Option[T]
def unapply(x: Short): Option[T]
def unapply(x: Byte): Option[T]
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].
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 wrap: ClassTag[Array[T]]

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

Deprecated Value Members

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
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
def arrayManifest: ClassManifest[Array[T]]

Definition Classes
ClassManifestDeprecatedApis
Annotations
@deprecated
Deprecated
(Since version 2.10.0) Use wrap instead
def erasure: Class[_]

Definition Classes
ClassManifestDeprecatedApis
Annotations
@deprecated
Deprecated
(Since version 2.10.0) Use runtimeClass instead
def newArray2(len: Int): Array[Array[T]]

Definition Classes
ClassManifestDeprecatedApis
Annotations
@deprecated
Deprecated
(Since version 2.10.0) Use wrap.newArray instead
def newArray3(len: Int): Array[Array[Array[T]]]

Definition Classes
ClassManifestDeprecatedApis
Annotations
@deprecated
Deprecated
(Since version 2.10.0) Use wrap.wrap.newArray instead
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
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
def newArrayBuilder(): ArrayBuilder[T]

Definition Classes
ClassManifestDeprecatedApis
Annotations
@deprecated
Deprecated
(Since version 2.10.0) Use ArrayBuilder.make(this) instead
def newWrappedArray(len: Int): WrappedArray[T]

Definition Classes
ClassManifestDeprecatedApis
Annotations
@deprecated
Deprecated
(Since version 2.10.0) Create WrappedArray directly instead
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

Related Docs: object ClassTag | package reflect

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

Abstract Value Members

abstract def runtimeClass: Class[_]

Concrete Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

def argString: String

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

final def asInstanceOf[T0]: T0

def canEqual(x: Any): Boolean

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(x: Any): Boolean

def finalize(): Unit

final def getClass(): Class[_]

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

final def ne(arg0: AnyRef): Boolean

def newArray(len: Int): Array[T]

final def notify(): Unit

final def notifyAll(): Unit

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

def toString(): String

def unapply(x: Unit): Option[T]

def unapply(x: Boolean): Option[T]

def unapply(x: Double): Option[T]

def unapply(x: Float): Option[T]

def unapply(x: Long): Option[T]

def unapply(x: Int): Option[T]

def unapply(x: Char): Option[T]

def unapply(x: Short): Option[T]

def unapply(x: Byte): Option[T]

def unapply(x: Any): Option[T]

final def wait(): Unit

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

final def wait(arg0: Long): Unit

def wrap: ClassTag[Array[T]]

Deprecated Value Members

def <:<(that: ClassManifest[_]): Boolean

def >:>(that: ClassManifest[_]): Boolean

def arrayManifest: ClassManifest[Array[T]]

def erasure: Class[_]

def newArray2(len: Int): Array[Array[T]]

def newArray3(len: Int): Array[Array[Array[T]]]

def newArray4(len: Int): Array[Array[Array[Array[T]]]]

def newArray5(len: Int): Array[Array[Array[Array[Array[T]]]]]

def newArrayBuilder(): ArrayBuilder[T]

def newWrappedArray(len: Int): WrappedArray[T]

def typeArguments: List[OptManifest[_]]

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

Ungrouped