ClassTag

@nowarn("cat=deprecation&origin=scala\\.reflect\\.ClassManifestDeprecatedApis") @implicitNotFound(msg = "No ClassTag available for ${T}")

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.

Companion:
object
Source:
ClassTag.scala
trait Manifest[T]

Value members

Abstract methods

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.

Source:
ClassTag.scala

Concrete methods

override 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.

Value parameters:
that

the value being probed for possible equality

Returns:

true if this instance can possibly equal that, otherwise false

Definition Classes
Source:
ClassTag.scala
override def equals(x: Any): Boolean

The universal equality method defined in AnyRef.

The universal equality method defined in AnyRef.

Definition Classes
Source:
ClassTag.scala
override def hashCode: Int

Calculate a hash code value for the object.

Calculate a hash code value for the object.

The default hashing algorithm is platform dependent.

Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)) yet not be equal (o1.equals(o2) returns false). A degenerate implementation could always return 0. However, it is required that if two objects are equal (o1.equals(o2) returns true) that they have identical hash codes (o1.hashCode.equals(o2.hashCode)). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the equals method.

Returns:

the hash code value for this object.

Definition Classes
Source:
ClassTag.scala
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

Source:
ClassTag.scala
override def toString: String

Returns a string representation of the object.

Returns a string representation of the object.

The default representation is platform dependent.

Returns:

a string representation of the object.

Definition Classes
Source:
ClassTag.scala
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].

Source:
ClassTag.scala

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

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

Source:
ClassTag.scala

Inherited methods

Deprecated and Inherited methods

@deprecated("use scala.reflect.runtime.universe.TypeTag for subtype checking instead", "2.10.0")
def <:<(that: ClassTag[_]): 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.

Deprecated
Inherited from:
ClassManifestDeprecatedApis
Source:
ClassManifestDeprecatedApis.scala
@deprecated("use scala.reflect.runtime.universe.TypeTag for subtype checking instead", "2.10.0")
def >:>(that: ClassTag[_]): 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.

Deprecated
Inherited from:
ClassManifestDeprecatedApis
Source:
ClassManifestDeprecatedApis.scala
@deprecated("use wrap instead", "2.10.0")
@deprecated("use runtimeClass instead", "2.10.0")
def erasure: Class[_]
@deprecated("use wrap.newArray instead", "2.10.0")
def newArray2(len: Int): Array[Array[T]]
@deprecated("use wrap.wrap.newArray instead", "2.10.0")
def newArray3(len: Int): Array[Array[Array[T]]]
@deprecated("use wrap.wrap.wrap.newArray instead", "2.10.0")
def newArray4(len: Int): Array[Array[Array[Array[T]]]]
@deprecated("use wrap.wrap.wrap.wrap.newArray instead", "2.10.0")
@deprecated("use ArrayBuilder.make(this) instead", "2.10.0")
@deprecated("create WrappedArray directly instead", "2.10.0")
@deprecated("use scala.reflect.runtime.universe.TypeTag to capture type structure instead", "2.10.0")