A TypeTag is a scala.reflect.api.TypeTags#WeakTypeTag with the additional
static guarantee that all type references are concrete, i.e.
A TypeTag is a scala.reflect.api.TypeTags#WeakTypeTag with the additional
static guarantee that all type references are concrete, i.e. it does not contain any references to
unresolved type parameters or abstract types.
If an implicit value of type WeakTypeTag[T] is required, the compiler will create one,
and the reflective representation of T can be accessed via the tpe field.
If an implicit value of type WeakTypeTag[T] is required, the compiler will create one,
and the reflective representation of T can be accessed via the tpe field.
Components of T can be references to type parameters or abstract types. Note that WeakTypeTag
makes an effort to be as concrete as possible, i.e. if TypeTags are available for the referenced type arguments
or abstract types, they are used to embed the concrete types into the WeakTypeTag. Otherwise the WeakTypeTag will
contain a reference to an abstract type. This behavior can be useful, when one expects T to be perhaps be partially
abstract, but requires special care to handle this case. However, if T is expected to be fully known, use
scala.reflect.api.TypeTags#TypeTag instead, which statically guarantees this property.
For more information about TypeTags, see the
Reflection Guide: TypeTags
Type symbol of x as derived from a type tag.
Test two objects for inequality.
Test two objects for inequality.
true if !(this == that), false otherwise.
Equivalent to x.hashCode except for boxed numeric types and null.
Equivalent to x.hashCode except for boxed numeric types and null.
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.
For null returns a hashcode where null.hashCode throws a
NullPointerException.
a hash value consistent with ==
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
true if the receiver object is equivalent to the argument; false otherwise.
Type tags corresponding to primitive types and constructor/extractor for WeakTypeTags.
Type tags corresponding to primitive types and constructor/extractor for WeakTypeTags.
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 a ClassCastException at
runtime, while the expression List(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.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
a copy of the receiver object.
not specified by SLS as a member of AnyRef
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 of AnyRef, and has three additional properties:
x and y of type AnyRef, multiple invocations of
x.eq(y) consistently returns true or consistently returns false.x of type AnyRef, x.eq(null) and null.eq(x) returns false.null.eq(null) returns true. When overriding the equals or hashCode 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).
true if the argument is a reference to the receiver object; false otherwise.
The equality method for reference types.
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 between finalize and non-local returns
and exceptions, are all platform dependent.
not specified by SLS as a member of AnyRef
A representation that corresponds to the dynamic class of the receiver object.
A representation that corresponds to the dynamic class of the receiver object.
The nature of the representation is platform dependent.
a representation that corresponds to the dynamic class of the receiver object.
not specified by SLS as a member of AnyRef
The hashCode method for reference types.
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 return false, while the
expression List(1).isInstanceOf[List[String]] will return true.
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.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Equivalent to !(this eq that).
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
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.
not specified by SLS as a member of AnyRef
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.
not specified by SLS as a member of AnyRef
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
a String representation of the object.
Shortcut for implicitly[TypeTag[T]].tpe
Shortcut for implicitly[TypeTag[T]]
Shortcut for implicitly[WeakTypeTag[T]].tpe
Shortcut for implicitly[WeakTypeTag[T]]
A
TypeTag[T]encapsulates the runtime type representation of some typeT. Like scala.reflect.Manifest, the prime use case ofTypeTags is to give access to erased types. However,TypeTags should be considered to be a richer replacement of the pre-2.10 notion of a Manifest, that are, in addition, fully integrated with Scala reflection.There exist three different types of
TypeTags:A full type descriptor of a Scala type. For example, a
TypeTag[List[String]]contains all type information, in this case, of typescala.List[String].A partial type descriptor of a Scala type. For example, a
ClassTag[List[String]]contains only the erased class type information, in this case, of typescala.collection.immutable.List.ClassTags provide access only to the runtime class of a type. Analogous to scala.reflect.ClassManifestA type descriptor for abstract types (see description below).
Like Manifests,
TypeTags are always generated by the compiler, and can be obtained in three ways:#1 Via the methods typeTag, classTag, or weakTypeTag
For example:
Each of these methods constructs a
TypeTag[T]orClassTag[T]for the given type argumentT.#2 Using an implicit parameter of type
TypeTag[T],ClassTag[T], orWeakTypeTag[T]For example:
#3 Context bound of a type parameter
...on methods or classes. The above example can be implemented as follows:
WeakTypeTagsWeakTypeTag[T]generalizesTypeTag[T]. Unlike a regularTypeTag, components of its type representation can be references to type parameters or abstract types. However,WeakTypeTag[T]tries to be as concrete as possible, i.e. if type tags are available for the referenced type arguments or abstract types, they are used to embed the concrete types into theWeakTypeTag[T].Continuing the example above:
TypeTags and Manifests
TypeTags correspond loosely to the pre-2.10 notion of scala.reflect.Manifests. While scala.reflect.ClassTag corresponds to scala.reflect.ClassManifest and scala.reflect.api.TypeTags#TypeTag mostly corresponds to scala.reflect.Manifest, other pre-2.10Manifesttypes do not have a direct correspondence with a 2.10 "Tag" type.This is because
Tags can reify arbitrary types, so they are always available. -Instead, one can compare their
Tagwith one of the baseTags (defined in the corresponding companion objects) in order to find out whether or not it represents a primitive value class. Additionally, it's possible to simply use<tag>.tpe.typeSymbol.isPrimitiveValueClass.Manifestcompanion objects.Instead, one could generate corresponding types using the reflection APIs provided by Java (for classes) and Scala (for types).
Instead, one could use the reflection APIs provided by Java (for classes) and Scala (for types).
In Scala 2.10, scala.reflect.ClassManifests are deprecated, and it is planned to deprecate scala.reflect.Manifest in favor of
TypeTags andClassTags in an upcoming point release. Thus, it is advisable to migrate anyManifest-based APIs to useTags.For more information about
TypeTags, see the Reflection Guide: TypeTagsscala.reflect.ClassTag, scala.reflect.api.TypeTags#TypeTag, scala.reflect.api.TypeTags#WeakTypeTag