A TypeTag
is a scala.reflect.api.TypeTags#WeakTypeTag with the additional
static guarantee that all type references are concrete, i.
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.
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 ==
Test two objects for equality.
Test two objects for equality.
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.
if the receiver object is not an instance of the erasure of type T0
.
Create a copy of the receiver object.
Tests whether the argument (arg0
) is a reference to the receiver object (this
).
Tests whether the argument (arg0
) 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.
Returns string formatted according to given format
string.
Returns string formatted according to given format
string.
Format strings are as for String.format
(@see java.lang.String.format).
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]]
(typeTags: StringAdd).self
(typeTags: StringFormat).self
(typeTags: ArrowAssoc[TypeTags]).x
(Since version 2.10.0) Use leftOfArrow
instead
(typeTags: Ensuring[TypeTags]).x
(Since version 2.10.0) Use resultOfEnsuring
instead
A
TypeTag[T]
encapsulates the runtime type representation of some typeT
. Like scala.reflect.Manifest, the prime use case ofTypeTag
s is to give access to erased types. However,TypeTag
s 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
.ClassTag
s 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,
TypeTag
s 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:
WeakTypeTag
sWeakTypeTag[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
TypeTag
s 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-2.10Manifest
types do not have a direct correspondence with a 2.10 "Tag
" type.This is because
Tag
s can reify arbitrary types, so they are always available. -Instead, one can compare their
Tag
with one of the baseTag
s (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
.Manifest
companion objects.Instead, one could generate corresponding types using the reflection APIs provided by Java (for classes) and Scala (for types).
Instead, one culd 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
TypeTag
s andClassTag
s in an upcoming point release. Thus, it is advisable to migrate anyManifest
-based APIs to useTag
s.For more information about
TypeTag
s, see the Reflection Guide: TypeTagsscala.reflect.ClassTag, scala.reflect.api.TypeTags#TypeTag, scala.reflect.api.TypeTags#WeakTypeTag