Trait scala.reflect.ClassTag

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

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.

Abstract methods

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def runtimeClass: Class[_]

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

Concrete methods

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override def canEqual(x: Any): Boolean

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override def equals(x: Any): Boolean

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override def hashCode: Int

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

Produces a new array with element type T and length len

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override def toString: String

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

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def wrap: ClassTag[Array[T]]

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

Inherited methods

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protected def argString: String

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protected def arrayClass[A](tp: Class[_]): Class[Array[A]]