Introduction to Scala Part2 : Collections

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List Traversable: Size Info Traversable: Element Retrieval Traversable: Addition Traversable: Conversion Traversable: Copying Operations Traversable: Map operations Traversable: Sub-collection retrieval operations Traversable: Folds Traversable: Subdivision operations

Traversable : Conversion

Operations:
- toArray,
- toList,
- toIterable,
- toSeq,
- toIndexedSeq,
- toStream,
- toSet,
- toMap
Goal: turn a Traversable collection into something more specific.

All these conversions return their receiver argument unchanged if the run-time type of the collection already matches the demanded collection type. For instance, applying toList to a list will yield the list itself.

> List(1, 2, 4).toArray
res0: Array[Int] = Array(1, 2, 4)

convert Iterable -> List

convert List -> Iterable

convert Seq -> List

convert List -> Seq

convert Array -> List

convert List of Int -> Array of Int

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package fp101.tp02.collections
import scala.reflect.ClassTag
object ExerciceConversion {
  /**
   *
   * Simples conversions
   *
   */
  def fromIterableToList[T](i: Iterable[T]): List[T] = ???
  def fromListToIterable[T](l: List[T]): Iterable[T] = ???
  def fromSeqToList[T](s: Seq[T]): List[T] = ???
  def fromListToSeq[T](l: List[T]): Seq[T] = ???
  def fromArrayToList[T](a: Array[T]): List[T] = ???
  /**
   * Note:
   * 
   * To create a generic method (instantiating an array of T where T is a type parameter),
   * It is more difficult because of the implementation of Array in Java that had runtime-safe arrays before it had compiletime parametric polymorphism.
   * 
   *  Scala needs at runtime to have information about T, in the form of an implicit value of type ClassTag[T]
   * 
   *   def fromListToArray[T](l: List[T])(implicit ev: ClassTag[T]): Array[T] = l.toArray 
   * 
   * This is an advance concept that will not be treated here.
   * 
   * Please, convert this List of Int in Array of Int
   */
  def fromIntListToIntArray(l: List[Int]): Array[Int] = ???
}

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