scala.collection.generic

# IsTraversableLike

#### trait IsTraversableLike[Repr] extends AnyRef

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:

1. type member `A`, which represents the element type of the target `GenTraversableLike[A, Repr]`
2. 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]]
    }

Since

  2.10

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2. AnyRef
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Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

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### Type Members

1. #### abstract type A

   The type of elements we can traverse over.

### Abstract Value Members

1. #### abstract val conversion: (Repr) ⇒ GenTraversableLike[A, Repr]

   A conversion from the representation type `Repr` to a `GenTraversableLike[A,Repr]`.

### Concrete Value Members

1. #### final def !=(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

2. #### final def ##(): Int

   Definition Classes
     AnyRef → Any

3. #### def +(other: String): String

   Implicit information
     This member is added by an implicit conversion from IsTraversableLike[Repr] to any2stringadd[IsTraversableLike[Repr]] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd

4. #### def ->[B](y: B): (IsTraversableLike[Repr], B)

   Implicit information
     This member is added by an implicit conversion from IsTraversableLike[Repr] to ArrowAssoc[IsTraversableLike[Repr]] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()

5. #### final def ==(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

6. #### final def asInstanceOf[T0]: T0

   Definition Classes
     Any

7. #### def clone(): AnyRef

   Attributes
     protected[java.lang]
   Definition Classes
     AnyRef
   Annotations
     @throws( ... )

8. #### def ensuring(cond: (IsTraversableLike[Repr]) ⇒ Boolean, msg: ⇒ Any): IsTraversableLike[Repr]

   Implicit information
     This member is added by an implicit conversion from IsTraversableLike[Repr] to Ensuring[IsTraversableLike[Repr]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring

9. #### def ensuring(cond: (IsTraversableLike[Repr]) ⇒ Boolean): IsTraversableLike[Repr]

   Implicit information
     This member is added by an implicit conversion from IsTraversableLike[Repr] to Ensuring[IsTraversableLike[Repr]] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring

10. #### def ensuring(cond: Boolean, msg: ⇒ Any): IsTraversableLike[Repr]

    Implicit information
      This member is added by an implicit conversion from IsTraversableLike[Repr] to Ensuring[IsTraversableLike[Repr]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

11. #### def ensuring(cond: Boolean): IsTraversableLike[Repr]

    Implicit information
      This member is added by an implicit conversion from IsTraversableLike[Repr] to Ensuring[IsTraversableLike[Repr]] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

12. #### final def eq(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

13. #### def equals(arg0: Any): Boolean

    Definition Classes
      AnyRef → Any

14. #### def finalize(): Unit

    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )

15. #### def formatted(fmtstr: String): String

    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).

    Implicit information
      This member is added by an implicit conversion from IsTraversableLike[Repr] to StringFormat[IsTraversableLike[Repr]] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()

16. #### final def getClass(): Class[_]

    Definition Classes
      AnyRef → Any

17. #### def hashCode(): Int

    Definition Classes
      AnyRef → Any

18. #### final def isInstanceOf[T0]: Boolean

    Definition Classes
      Any

19. #### final def ne(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

20. #### final def notify(): Unit

    Definition Classes
      AnyRef

21. #### final def notifyAll(): Unit

    Definition Classes
      AnyRef

22. #### final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
      AnyRef

23. #### def toString(): String

    Definition Classes
      AnyRef → Any

24. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

25. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

26. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

27. #### def →[B](y: B): (IsTraversableLike[Repr], B)

    Implicit information
      This member is added by an implicit conversion from IsTraversableLike[Repr] to ArrowAssoc[IsTraversableLike[Repr]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from IsTraversableLike[Repr] to any2stringadd[IsTraversableLike[Repr]]

### Inherited by implicit conversion StringFormat from IsTraversableLike[Repr] to StringFormat[IsTraversableLike[Repr]]

### Inherited by implicit conversion Ensuring from IsTraversableLike[Repr] to Ensuring[IsTraversableLike[Repr]]

### Inherited by implicit conversion ArrowAssoc from IsTraversableLike[Repr] to ArrowAssoc[IsTraversableLike[Repr]]

### Ungrouped