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 Array
s whose element types are unknown
at compile time.
ClassTag
s 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, ClassTag
s 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
- Alphabetic
- By Inheritance
- ClassTag
- Equals
- ClassManifestDeprecatedApis
- OptManifest
- Serializable
- Serializable
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
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- Public
- All
Abstract Value Members
-
abstract
def
runtimeClass: Class[_]
A class representing the type
U
to whichT
would be erased.A class representing the type
U
to whichT
would be erased. Note that there is no subtyping relationship betweenT
andU
.
Concrete Value Members
-
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
-
final
def
##(): Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. 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. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
-
def
+(other: String): String
- Implicit
- 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
-
def
->[B](y: B): (ClassTag[T], B)
- Implicit
- 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()
-
final
def
==(arg0: Any): Boolean
The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.- returns
true
if the receiver object is equivalent to the argument;false
otherwise.
- 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
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 aClassCastException
at runtime, while the expressionList(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 typeT0
.
-
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
Create a copy of the receiver object.
-
def
ensuring(cond: (ClassTag[T]) ⇒ Boolean, msg: ⇒ Any): ClassTag[T]
- Implicit
- 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
-
def
ensuring(cond: (ClassTag[T]) ⇒ Boolean): ClassTag[T]
- Implicit
- 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
-
def
ensuring(cond: Boolean, msg: ⇒ Any): ClassTag[T]
- Implicit
- 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
-
def
ensuring(cond: Boolean): ClassTag[T]
- Implicit
- 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
-
final
def
eq(arg0: AnyRef): Boolean
Tests whether the argument (
that
) is a reference to the receiver object (this
).Tests whether the argument (
that
) is a reference to the receiver object (this
).The
eq
method implements an equivalence relation on non-null instances ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
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
- It is consistent: for any non-null instances
-
def
equals(x: Any): Boolean
The universal equality method defined in
AnyRef
. -
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 betweenfinalize
and non-local returns and exceptions, are all platform dependent.- Attributes
- protected[lang]
- Definition Classes
- AnyRef
- Annotations
- @throws( classOf[java.lang.Throwable] )
- Note
not specified by SLS as a member of AnyRef
-
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 forString.format
(@see java.lang.String.format).- Implicit
- 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()
-
final
def
getClass(): Class[_]
Returns the runtime class representation of the object.
-
def
hashCode(): Int
The hashCode method for reference types.
-
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 returnfalse
, while the expressionList(1).isInstanceOf[List[String]]
will returntrue
. 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 typeT0
;false
otherwise.
- Definition Classes
- Any
-
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
-
def
newArray(len: Int): Array[T]
Produces a new array with element type
T
and lengthlen
Produces a new array with element type
T
and lengthlen
- Definition Classes
- ClassTag → ClassManifestDeprecatedApis
-
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
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
-
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
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
-
def
toString(): String
Creates a String representation of this object.
-
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 asct(_: T)
, wherect
is theClassTag[T]
instance. Type tests necessary before calling other extractors are treated similarly.SomeExtractor(...)
is turned intoct(SomeExtractor(...))
ifT
inSomeExtractor.unapply(x: T)
is uncheckable, but we have an instance ofClassTag[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
-
def
wrap: ClassTag[Array[T]]
Produces a
ClassTag
that knows how to instantiate anArray[Array[T]]
-
def
→[B](y: B): (ClassTag[T], B)
- Implicit
- 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
-
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
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.collection.parallel.immutable
- Immutable, parallel data-structures such asParVector
,ParRange
,ParHashMap
orParHashSet
scala.collection.parallel.mutable
- Mutable, parallel data-structures such asParArray
,ParHashMap
,ParTrieMap
orParHashSet
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect
- Scala's reflection API (scala-reflect.jar)scala.xml
- XML parsing, manipulation, and serialization (scala-xml.jar)scala.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)scala.util.parsing
- Parser combinators (scala-parser-combinators.jar)Automatic imports
Identifiers in the scala package and the
scala.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.