A mixin trait that implements index flag behaviour using atomic integers. The setIndex
operation is wait-free, while conditional set operations setIndexIfGreater
and setIndexIfLesser
are lock-free and support only monotonic changes.
A base trait for builder factories.
the type of the underlying collection that requests a builder to be created.
the element type of the collection to be created.
the type of the collection to be created.
2.8
A base trait for parallel builder factories.
the type of the underlying collection that requests a builder to be created.
the element type of the collection to be created.
the type of the collection to be created.
2.8
This trait forms part of collections that can be cleared with a clear() call.
2.10
A template for companion objects of Seq and subclasses thereof.
2.8
A template for companion objects of Traversable
and subclasses thereof. This class provides a set of operations to create
objects. It is typically inherited by companion objects of subclasses of Traversable
Traversable
.
2.8
This trait represents collections classes which require class tags for their element types.
2.8
A template class for companion objects of "regular" collection classes represent an unconstrained higher-kinded type. Typically such classes inherit from trait GenericTraversableTemplate
.
The type constructor representing the collection class.
2.8
This class represents companions of classes which require the ordered trait for their element types.
2.8
A template class for companion objects of parallel collection classes. They should be mixed in together with GenericCompanion
type.
A template trait for collections having a companion.
the element type of the collection
the type constructor representing the collection class
2.8
2.8
A template class for companion objects of
collection classes that represent an unconstrained higher-kinded type. regular
The type of the collection elements.
The type constructor representing the collection class.
2.8
This trait forms part of collections that can be augmented using a +=
operator and that can be cleared of all elements using a clear
method.
2.8
2.8
A template for companion objects of immutable.Map
and subclasses thereof.
2.8
A template for companion objects of SortedMap
and subclasses thereof.
2.8
A template for companion objects of SortedSet
and subclasses thereof.
2.8
A template for companion objects of IndexedSeq and subclasses thereof.
2.11
Type class witnessing that a collection representation type Repr
has elements of type A
and has a conversion to SeqLike[A, Repr]
.
This type enables simple enrichment of Seq
s with extension methods which can make full use of the mechanics of the Scala collections framework in their implementation.
Example usage:
class FilterMapImpl[A, Repr](val r: SeqLike[A, Repr]) { final def filterMap[B, That](f: A => Option[B])(implicit cbf: CanBuildFrom[Repr, B, That]): That = r.flatMap(f(_)) } implicit def filterMap[Repr, A](r: Repr)(implicit fr: IsSeqLike[Repr]): FilterMapImpl[fr.A,Repr] = new FilterMapImpl(fr.conversion(r)) val l = List(1, 2, 3, 4, 5) List(1, 2, 3, 4, 5) filterMap (i => if(i % 2 == 0) Some(i) else None) // == List(2, 4)
A trait which can be used to avoid code duplication when defining extension methods that should be applicable both to existing Scala collections (i.e., types extending GenTraversableLike
) as well as other (potentially user-defined) types that could be converted to a Scala collection type. This trait makes it possible to treat Scala collections and types that can be implicitly converted to a collection type uniformly. For example, one can provide extension methods that work both on collection types and on String
s (String
s do not extend GenTraversableLike
, but can be converted to GenTraversableLike
)
IsTraversable
provides two members:
A
, which represents the element type of the target GenTraversableLike[A, Repr]
value member conversion
, which provides a way to convert between the type we wish to add extension methods to, Repr
, and GenTraversableLike[A, Repr]
.One must provide IsTraversableLike
as an implicit parameter type of an implicit conversion. Its usage is shown below. Our objective in the following example is to provide a generic extension method mapReduce
to any type that extends or can be converted to GenTraversableLike
. In our example, this includes String
.
import scala.collection.GenTraversableLike import scala.collection.generic.IsTraversableLike class ExtensionMethods[A, Repr](coll: GenTraversableLike[A, Repr]) { def mapReduce[B](mapper: A => B)(reducer: (B, B) => B): B = { val iter = coll.toIterator var res = mapper(iter.next()) while (iter.hasNext) res = reducer(res, mapper(iter.next())) res } } implicit def withExtensions[Repr](coll: Repr)(implicit traversable: IsTraversableLike[Repr]) = new ExtensionMethods(traversable.conversion(coll)) // See it in action! List(1, 2, 3).mapReduce(_ * 2)(_ + _) // res0: Int = 12 "Yeah, well, you know, that's just, like, your opinion, man.".mapReduce(x => 1)(_ + _) // res1: Int = 59
Here, we begin by creating a class ExtensionMethods
which contains our mapReduce
extension method. Note that ExtensionMethods
takes a constructor argument coll
of type GenTraversableLike[A, Repr]
, where A
represents the element type and Repr
represents (typically) the collection type. The implementation of mapReduce
itself is straightforward.
The interesting bit is the implicit conversion withExtensions
, which returns an instance of ExtensionMethods
. This implicit conversion can only be applied if there is an implicit value traversable
of type IsTraversableLike[Repr]
in scope. Since IsTraversableLike
provides value member conversion
, which gives us a way to convert between whatever type we wish to add an extension method to (in this case, Repr
) and GenTraversableLike[A, Repr]
, we can now convert coll
from type Repr
to GenTraversableLike[A, Repr]
. This allows us to create an instance of the ExtensionMethods
class, which we pass our new GenTraversableLike[A, Repr]
to.
When the mapReduce
method is called on some type of which it is not a member, implicit search is triggered. Because implicit conversion withExtensions
is generic, it will be applied as long as an implicit value of type IsTraversableLike[Repr]
can be found. Given that IsTraversableLike
contains implicit members that return values of type IsTraversableLike
, this requirement is typically satisfied, and the chain of interactions described in the previous paragraph is set into action. (See the IsTraversableLike
companion object, which contains a precise specification of the available implicits.)
Note: Currently, it's not possible to combine the implicit conversion and the class with the extension methods into an implicit class due to limitations of type inference.
IsTraversableLike
for New TypesOne must simply provide an implicit value of type IsTraversableLike
specific to the new type, or an implicit conversion which returns an instance of IsTraversableLike
specific to the new type.
Below is an example of an implementation of the IsTraversableLike
trait where the Repr
type is String
.
implicit val stringRepr: IsTraversableLike[String] { type A = Char } = new IsTraversableLike[String] { type A = Char val conversion = implicitly[String => GenTraversableLike[Char, String]] }
2.10
Type class witnessing that a collection representation type Repr
has elements of type A
and has a conversion to GenTraversableOnce[A]
.
This type enables simple enrichment of GenTraversableOnce
s with extension methods which can make full use of the mechanics of the Scala collections framework in their implementation.
Example usage,
class FilterMapImpl[A, Repr](val r: GenTraversableOnce[A]) { final def filterMap[B, That](f: A => Option[B])(implicit cbf: CanBuildFrom[Repr, B, That]): That = { val b = cbf() for(e <- r.seq) f(e) foreach (b +=) b.result } } implicit def filterMap[Repr, A](r: Repr)(implicit fr: IsTraversableOnce[Repr]): FilterMapImpl[fr.A,Repr] = new FilterMapImpl[fr.A, Repr](fr.conversion(r)) val l = List(1, 2, 3, 4, 5) List(1, 2, 3, 4, 5) filterMap (i => if(i % 2 == 0) Some(i) else None) // == List(2, 4)
2.10
A template for companion objects of mutable.Map
and subclasses thereof.
2.8
A template for companion objects of SortedMap
and subclasses thereof.
the type of the collection.
2.12
2.12
A template class for companion objects of ParIterable
and subclasses thereof. This class extends TraversableFactory
and provides a set of operations to create
objects.ParIterable
A template class for companion objects of ParMap
and subclasses thereof. This class extends TraversableFactory
and provides a set of operations to create
objects.ParMap
2.8
A template for companion objects of Seq and subclasses thereof.
2.8
This trait forms part of collections that can be reduced using a -=
operator.
2.8
A message interface serves as a unique interface to the part of the collection capable of receiving messages from a different task.
One example of use of this is the find
method, which can use the signalling interface to inform worker threads that an element has been found and no further search is necessary.
Any collection (including maps) whose keys (or elements) are ordered.
2.8
A template for companion objects of mutable.Map and subclasses thereof.
2.8
A template for companion objects of Set and subclasses thereof.
2.8
This trait represents collection-like objects that can be reduced using a '+' operator. It defines variants of -
and --
as convenience methods in terms of single-element removal -
.
the type of the elements of the collection.
the type of the collection itself
2.8
A template for companion objects of Traversable
and subclasses thereof. This class provides a set of operations to create Traversable
objects. It is typically inherited by companion objects of subclasses of Traversable
.
2.8
(Since version 2.10.0) use ClassTagTraversableFactory instead
(Since version 2.10.0) use GenericClassTagCompanion instead
(Since version 2.10.0) use GenericClassTagTraversableTemplate instead
This trait implements a forwarder for iterable objects. It forwards all calls to a different iterable object, except for
toString
, hashCode
, equals
, stringPrefix
newBuilder
, view
all calls creating a new iterable object of the same kindThe above methods are forwarded by subclass `IterableProxy`.
(Since version 2.11.0) forwarding is inherently unreliable since it is not automated and methods can be forgotten
2.8
This class implements a forwarder for sequences. It forwards all calls to a different sequence object except for
toString
, hashCode
, equals
, stringPrefix
newBuilder
, view
, toSeq
all calls creating a new sequence of the same kind The above methods are forwarded by subclass SeqProxy
.
(Since version 2.11.0) forwarding is inherently unreliable since it is not automated and new methods can be forgotten
2.8
This trait implements a forwarder for traversable objects. It forwards all calls to a different traversable, except for:
toString
, hashCode
, equals
, stringPrefix
newBuilder
, view
All calls creating a new traversable of the same kind.
(Since version 2.11.0) forwarding is inherently unreliable since it is not automated and new methods can be forgotten
2.8
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.12.9/scala/collection/generic/index.html