Package scala.collection.generic

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.

A base trait for parallel builder factories.

This trait forms part of collections that can be cleared with a clear() call.

A template for companion objects of Seq and subclasses thereof.

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.

This trait represents collections classes which require class tags for their element types.

A template class for companion objects of "regular" collection classes represent an unconstrained higher-kinded type. Typically such classes inherit from trait GenericTraversableTemplate.

This class represents companions of classes which require the ordered trait for their element types.

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.

A template class for companion objects of regular collection classes that represent an unconstrained higher-kinded type.

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.

A template for companion objects of immutable.Map and subclasses thereof.

A template for companion objects of SortedMap and subclasses thereof.

A template for companion objects of SortedSet and subclasses thereof.

A template for companion objects of IndexedSeq and subclasses thereof.

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 Seqs 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 Strings (Strings do not extend GenTraversableLike, but can be converted to GenTraversableLike)

IsTraversable provides two members:

type member 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].

Usage

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.

Implementing IsTraversableLike for New Types

One 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]]
  }

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 GenTraversableOnces 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)

A template for companion objects of mutable.Map and subclasses thereof.

A template for companion objects of SortedMap and subclasses thereof.

A template class for companion objects of ParIterable and subclasses thereof. This class extends TraversableFactory and provides a set of operations to create ParIterable objects.

A template class for companion objects of ParMap and subclasses thereof. This class extends TraversableFactory and provides a set of operations to create ParMap objects.

A template for companion objects of Seq and subclasses thereof.

This trait forms part of collections that can be reduced using a -= operator.

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.

A template for companion objects of mutable.Map and subclasses thereof.

A template for companion objects of Set and subclasses thereof.

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 -.

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.

This trait implements a forwarder for iterable objects. It forwards all calls to a different iterable object, except for

toString, hashCode, equals, stringPrefix newBuilder, viewall calls creating a new iterable object of the same kind

The above methods are forwarded by subclass `IterableProxy`.

This class implements a forwarder for sequences. It forwards all calls to a different sequence object except for

toString, hashCode, equals, stringPrefix newBuilder, view, toSeqall calls creating a new sequence of the same kind

The above methods are forwarded by subclass SeqProxy.

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.