W3cubDocs

/Scala 2.13 Library

Trait scala.collection.generic.IsIterable

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. 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]
  2. type member C, which represents the type returned by transformation operations that preserve the collection’s elements type
  3. 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)

Source
IsIterable.scala
Linear Supertypes
IsIterableOnce[Repr], AnyRef, Any
Known Subclasses
IsMap, IsSeq

Type Members

abstract type A

The type of elements we can traverse over (e.g. Int).

Definition Classes
IsIterableOnce

abstract type C

The type returned by transformation operations that preserve the same elements type (e.g. filter, take).

In practice, this type is often Repr itself, excepted in the case of SeqView[A] (and other View[A] subclasses), where it is “only” View[A].

Abstract Value Members

abstract def apply(coll: Repr): IterableOps[A, Iterable, C]

A conversion from the type Repr to IterableOps[A, Iterable, C]

Definition Classes
IsIterableIsIterableOnce

Concrete Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

true if !(this == that), false otherwise.

Definition Classes
AnyRef → Any

final def ##(): Int

Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

returns

a hash value consistent with ==

Definition Classes
AnyRef → Any

def +(other: String): String

Implicit
This member is added by an implicit conversion from IsIterable[Repr] toany2stringadd[IsIterable[Repr]] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

def ->[B](y: B): (IsIterable[Repr], B)

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

final def ==(arg0: Any): Boolean

The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

final def asInstanceOf[T0]: T0

Cast the receiver object to be of type T0.

Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

returns

the receiver object.

Definition Classes
Any
Exceptions thrown

ClassCastException if the receiver object is not an instance of the erasure of type T0.

def clone(): AnyRef

Create a copy of the receiver object.

The default implementation of the clone method is platform dependent.

returns

a copy of the receiver object.

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

not specified by SLS as a member of AnyRef

def ensuring(cond: (IsIterable[Repr]) => Boolean, msg: => Any): IsIterable[Repr]

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

def ensuring(cond: (IsIterable[Repr]) => Boolean): IsIterable[Repr]

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

def ensuring(cond: Boolean, msg: => Any): IsIterable[Repr]

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

def ensuring(cond: Boolean): IsIterable[Repr]

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

final def eq(arg0: AnyRef): Boolean

Tests whether the argument (that) is a reference to the receiver object (this).

The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false. null.eq(null) returns true.

When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

returns

true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

def equals(arg0: AnyRef): Boolean

The equality method for reference types. Default implementation delegates to eq.

See also equals in scala.Any.

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

def finalize(): Unit

Called by the garbage collector on the receiver object when there are no more references to the object.

The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

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

not specified by SLS as a member of AnyRef

def formatted(fmtstr: String): String

Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

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

final def getClass(): Class[_ <: AnyRef]

Returns the runtime class representation of the object.

returns

a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
Annotations
@native()

def hashCode(): Int

The hashCode method for reference types. See hashCode in scala.Any.

returns

the hash code value for this object.

Definition Classes
AnyRef → Any
Annotations
@native()

final def isInstanceOf[T0]: Boolean

Test whether the dynamic type of the receiver object is T0.

Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

returns

true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

final def notify(): Unit

Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def notifyAll(): Unit

Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def toString(): String

Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

returns

a String representation of the object.

Definition Classes
AnyRef → Any

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

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

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/collection/generic/IsIterable.html