Trait scala.reflect.Manifest

@nowarn("cat=deprecation&origin=scala\\.reflect\\.ClassManifest(DeprecatedApis.*)?") @implicitNotFound(msg = "No Manifest available for ${T}.")

trait Manifest[T] extends ClassTag[T] with Equals

A Manifest[T] is an opaque descriptor for type T. Its supported use is to give access to the erasure of the type as a Class instance, as is necessary for the creation of native Arrays if the class is not known at compile time.

The type-relation operators <:< and =:= should be considered approximations only, as there are numerous aspects of type conformance which are not yet adequately represented in manifests.

Example usages:

def arr[T] = new Array[T](0)                          // does not compile
def arr[T](implicit m: Manifest[T]) = new Array[T](0) // compiles
def arr[T: Manifest] = new Array[T](0)                // shorthand for the preceding

// Methods manifest and optManifest are in [[scala.Predef]].
def isApproxSubType[T: Manifest, U: Manifest] = manifest[T] <:< manifest[U]
isApproxSubType[List[String], List[AnyRef]] // true
isApproxSubType[List[String], List[Int]]    // false

def methods[T: Manifest] = manifest[T].runtimeClass.getMethods
def retType[T: Manifest](name: String) =
  methods[T] find (_.getName == name) map (_.getGenericReturnType)

retType[Map[_, _]]("values")  // Some(scala.collection.Iterable<B>)

Concrete methods

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override def arrayManifest: Manifest[Array[T]]

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override def canEqual(that: Any): Boolean

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override def equals(that: Any): Boolean

Note: testing for erasure here is important, as it is many times faster than <:< and rules out most comparisons.

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override def hashCode: Int

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override def typeArguments: List[Manifest[_]]

Inherited methods

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protected def argString: String

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

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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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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.

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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]]