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Scala 3/scala/scala.collection/scala.collection.generic

scala.collection.generic

package scala.collection.generic

Members list

Type members

Classlikes

trait DefaultSerializable extends Serializable

Mix-in trait to enable DefaultSerializationProxy for the standard collection types.

Mix-in trait to enable DefaultSerializationProxy for the standard collection types. Depending on the type it is mixed into, it will dynamically choose iterableFactory, mapFactory, sortedIterableFactory or sortedMapFactory for deserialization into the respective CC type. Override writeReplace or implement it directly without using this trait if you need a non-standard factory or if you want to use a different serialization scheme.

Attributes

Source
DefaultSerializationProxy.scala
Supertypes
trait Serializable
class Object
trait Matchable
class Any
Known subtypes
class TrieMap[K, V]
class HashMap[K, V]
class HashSet[A]
class List[A]
class ::[A]
object Nil.type
class ListMap[K, V]
class ListSet[A]
class Queue[A]
class TreeMap[K, V]
class TreeSet[A]
class Vector[A]
class ArrayBuffer[A]
class ArrayDeque[A]
class Queue[A]
class Stack[A]
class LinkedHashMap[K, V]
class LinkedHashSet[A]
class ListBuffer[A]
class ListMap[K, V]
class OpenHashMap[Key, Value]
class TreeMap[K, V]
class TreeSet[A]
class UnrolledBuffer[T]
Show all
Self type
final class DefaultSerializationProxy[A](factory: Factory[A, Any], coll: Iterable[A]) extends Serializable

The default serialization proxy for collection implementations.

The default serialization proxy for collection implementations.

This class is final and requires an extra Factory object rather than leaving the details of creating a Builder to an abstract method that could be implemented by a subclass. This is necessary because the factory is needed for deserializing this class's private state, which happens before any subclass fields would be deserialized. Any additional state required to create the proper Builder needs to be captured by the factory.

Attributes

Source
DefaultSerializationProxy.scala
Supertypes
trait Serializable
class Object
trait Matchable
class Any
trait IsIterable[Repr] extends IsIterableOnce[Repr]

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 Iterable) as well as other (potentially user-defined) types that could be converted to a Scala collection type.

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 Iterable) 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 Iterable, but can be converted to Iterable)

IsIterable provides three members:

1. type member A, which represents the element type of the target Iterable[A] 1. type member C, which represents the type returned by transformation operations that preserve the collection’s elements type 1. method apply, which provides a way to convert between the type we wish to add extension methods to, Repr, and IterableOps[A, Iterable, C].

Usage

One must provide IsIterable 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 Iterable. In our example, this includes String.

  import scala.collection.{Iterable, IterableOps}
  import scala.collection.generic.IsIterable

  class ExtensionMethods[Repr, I <: IsIterable[Repr]](coll: Repr, it: I) {
    def mapReduce[B](mapper: it.A => B)(reducer: (B, B) => B): B = {
      val iter = it(coll).iterator
      var res = mapper(iter.next())
      while (iter.hasNext)
        res = reducer(res, mapper(iter.next()))
      res
    }
  }

  implicit def withExtensions[Repr](coll: Repr)(implicit it: IsIterable[Repr]): ExtensionMethods[Repr, it.type] =
    new ExtensionMethods(coll, it)

// 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 Repr, where Repr represents (typically) the collection type, and an argument it of a subtype of IsIterable[Repr]. The body of the method starts by converting the coll argument to an IterableOps in order to call the iterator method on it. The remaining of the implementation is straightforward.

The withExtensions implicit conversion makes the mapReduce operation available on any type Repr for which it exists an implicit IsIterable[Repr] instance. Note how we keep track of the precise type of the implicit it argument by using the it.type singleton type, rather than the wider IsIterable[Repr] type. We do that so that the information carried by the type members A and C of the it argument is not lost.

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 IsIterable[Repr] can be found. Given that the IsIterable companion object contains implicit members that return values of type IsIterable, this requirement is typically satisfied, and the chain of interactions described in the previous paragraph is set into action. (See the IsIterable 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 IsIterable for New Types

One must simply provide an implicit value of type IsIterable specific to the new type, or an implicit conversion which returns an instance of IsIterable specific to the new type.

Below is an example of an implementation of the IsIterable trait where the Repr type is Range.

implicit val rangeRepr: IsIterable[Range] { type A = Int; type C = IndexedSeq[Int] } =
 new IsIterable[Range] {
   type A = Int
   type C = IndexedSeq[Int]
   def apply(coll: Range): IterableOps[Int, IndexedSeq, IndexedSeq[Int]] = coll
 }

(Note that in practice the IsIterable[Range] instance is already provided by the standard library, and it is defined as an IsSeq[Range] instance)

Attributes

Companion
object
Source
IsIterable.scala
Supertypes
trait IsIterableOnce[Repr]
class Object
trait Matchable
class Any
Known subtypes
trait IsMap[Repr]
trait IsSeq[Repr]
object IsIterable extends IsIterableLowPriority

Attributes

Companion
trait
Source
IsIterable.scala
Supertypes
class Object
trait Matchable
class Any
Self type
IsIterable.type
trait IsIterableLowPriority

Attributes

Source
IsIterable.scala
Supertypes
class Object
trait Matchable
class Any
Known subtypes
object IsIterable.type
trait IsIterableOnce[Repr]

Type class witnessing that a collection representation type Repr has elements of type A and has a conversion to IterableOnce[A].

Type class witnessing that a collection representation type Repr has elements of type A and has a conversion to IterableOnce[A].

This type enables simple enrichment of IterableOnces with extension methods which can make full use of the mechanics of the Scala collections framework in their implementation.

Example usage,

class FilterMapImpl[Repr, I <: IsIterableOnce[Repr]](coll: Repr, it: I) {
  final def filterMap[B, That](f: it.A => Option[B])(implicit bf: BuildFrom[Repr, B, That]): That = {
    val b = bf.newBuilder(coll)
    for(e <- it(coll).iterator) f(e) foreach (b +=)
    b.result()
  }
}
implicit def filterMap[Repr](coll: Repr)(implicit it: IsIterableOnce[Repr]): FilterMapImpl[Repr, it.type] =
  new FilterMapImpl(coll, it)

List(1, 2, 3, 4, 5) filterMap (i => if(i % 2 == 0) Some(i) else None)
// == List(2, 4)

Attributes

Companion
object
Source
IsIterableOnce.scala
Supertypes
class Object
trait Matchable
class Any
Known subtypes
trait IsIterable[Repr]
trait IsMap[Repr]
trait IsSeq[Repr]
object IsIterableOnce extends IsIterableOnceLowPriority

Attributes

Companion
trait
Source
IsIterableOnce.scala
Supertypes
class Object
trait Matchable
class Any
Self type
trait IsIterableOnceLowPriority

Attributes

Source
IsIterableOnce.scala
Supertypes
class Object
trait Matchable
class Any
Known subtypes
object IsIterableOnce.type
trait IsMap[Repr] extends IsIterable[Repr]

Type class witnessing that a collection type Repr has keys of type K, values of type V and has a conversion to MapOps[K, V, Iterable, C], for some types K, V and C.

Type class witnessing that a collection type Repr has keys of type K, values of type V and has a conversion to MapOps[K, V, Iterable, C], for some types K, V and C.

This type enables simple enrichment of Maps with extension methods.

Type parameters

Repr

Collection type (e.g. Map[Int, String])

Attributes

See also
Companion
object
Source
IsMap.scala
Supertypes
trait IsIterable[Repr]
trait IsIterableOnce[Repr]
class Object
trait Matchable
class Any
object IsMap

Attributes

Companion
trait
Source
IsMap.scala
Supertypes
class Object
trait Matchable
class Any
Self type
IsMap.type
trait IsSeq[Repr] extends IsIterable[Repr]

Type class witnessing that a collection representation type Repr has elements of type A and has a conversion to SeqOps[A, Iterable, C], for some types A and C.

Type class witnessing that a collection representation type Repr has elements of type A and has a conversion to SeqOps[A, Iterable, C], for some types A and C.

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.

Attributes

See also
Companion
object
Source
IsSeq.scala
Supertypes
trait IsIterable[Repr]
trait IsIterableOnce[Repr]
class Object
trait Matchable
class Any
object IsSeq

Attributes

Companion
trait
Source
IsSeq.scala
Supertypes
class Object
trait Matchable
class Any
Self type
IsSeq.type

Deprecated classlikes

trait Subtractable[A, +Repr <: Subtractable[A, Repr]]

This trait represents collection-like objects that can be reduced using a '+' operator.

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 -.

Type parameters

A

the type of the elements of the $coll.

Repr

the type of the $coll itself

Attributes

Deprecated
true
Source
Subtractable.scala
Supertypes
class Object
trait Matchable
class Any
Self type
Subtractable[A, Repr]

Deprecated types

type CanBuildFrom[-From, -A, +C] = BuildFrom[From, A, C]

Attributes

Deprecated
true
Source
package.scala
type Clearable = Clearable

Attributes

Deprecated
true
Source
package.scala
type Growable[-A] = Growable[A]

Attributes

Deprecated
true
Source
package.scala
type IsTraversableLike[Repr] = IsIterable[Repr]

Attributes

Deprecated
true
Source
package.scala
type IsTraversableOnce[Repr] = IsIterableOnce[Repr]

Attributes

Deprecated
true
Source
package.scala
type Shrinkable[-A] = Shrinkable[A]

Attributes

Deprecated
true
Source
package.scala
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Copyright (c) 2002-2022, LAMP/EPFL
Copyright (c) 2002-2022, LAMP/EPFL