Class scala.Option

@SerialVersionUID(-114498752079829388L)

sealed abstract class Option[+A] extends IterableOnce[A] with Product with Serializable

Represents optional values. Instances of Option are either an instance of scala.Some or the object None.

The most idiomatic way to use an scala.Option instance is to treat it as a collection or monad and use map,flatMap, filter, or foreach:

val name: Option[String] = request getParameter "name"
val upper = name map { _.trim } filter { _.length != 0 } map { _.toUpperCase }
println(upper getOrElse "")

Note that this is equivalent to

val upper = for {
  name <- request getParameter "name"
  trimmed <- Some(name.trim)
  upper <- Some(trimmed.toUpperCase) if trimmed.length != 0
} yield upper
println(upper getOrElse "")

Because of how for comprehension works, if None is returned from request.getParameter, the entire expression results in None

This allows for sophisticated chaining of scala.Option values without having to check for the existence of a value.

These are useful methods that exist for both scala.Some and None. - isDefined — True if not empty - isEmpty — True if empty - nonEmpty — True if not empty - orElse — Evaluate and return alternate optional value if empty - getOrElse — Evaluate and return alternate value if empty - get — Return value, throw exception if empty - fold — Apply function on optional value, return default if empty - map — Apply a function on the optional value - flatMap — Same as map but function must return an optional value - foreach — Apply a procedure on option value - collect — Apply partial pattern match on optional value - filter — An optional value satisfies predicate - filterNot — An optional value doesn't satisfy predicate - exists — Apply predicate on optional value, or false if empty - forall — Apply predicate on optional value, or true if empty - contains — Checks if value equals optional value, or false if empty - zip — Combine two optional values to make a paired optional value - unzip — Split an optional pair to two optional values - unzip3 — Split an optional triple to three optional values - toList — Unary list of optional value, otherwise the empty list

A less-idiomatic way to use scala.Option values is via pattern matching:

val nameMaybe = request getParameter "name"
nameMaybe match {
  case Some(name) =>
    println(name.trim.toUppercase)
  case None =>
    println("No name value")
}

Interacting with code that can occasionally return null can be safely wrapped in scala.Option to become None and scala.Some otherwise.

val abc = new java.util.HashMap[Int, String]
abc.put(1, "A")
bMaybe = Option(abc.get(2))
bMaybe match {
 case Some(b) =>
   println(s"Found $b")
 case None =>
   println("Not found")
}

Classlikes

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class WithFilter(p: A => Boolean)

We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.

Abstract methods

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def get: A

Returns the option's value.

This is equivalent to:

option match {
 case Some(x) => x
 case None    => throw new Exception
}

Concrete methods

Source@inline

final def collect[B](pf: PartialFunction[A, B]): Option[B]

Returns a scala.Some containing the result of applying pf to this scala.Option's contained value, if this option is nonempty and pf is defined for that value. Returns None otherwise.

// Returns Some(HTTP) because the partial function covers the case.
Some("http") collect {case "http" => "HTTP"}
// Returns None because the partial function doesn't cover the case.
Some("ftp") collect {case "http" => "HTTP"}
// Returns None because the option is empty. There is no value to pass to the partial function.
None collect {case value => value}

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final def contains[A1 >: A](elem: A1): Boolean

Tests whether the option contains a given value as an element.

This is equivalent to:

option match {
 case Some(x) => x == elem
 case None    => false
}

// Returns true because Some instance contains string "something" which equals "something".
Some("something") contains "something"
// Returns false because "something" != "anything".
Some("something") contains "anything"
// Returns false when method called on None.
None contains "anything"

Source@inline

final def exists(p: A => Boolean): Boolean

Returns true if this option is nonempty and the predicate p returns true when applied to this scala.Option's value. Otherwise, returns false.

This is equivalent to:

option match {
 case Some(x) => p(x)
 case None    => false
}

Source@inline

final def filter(p: A => Boolean): Option[A]

Returns this scala.Option if it is nonempty and applying the predicate p to this scala.Option's value returns true. Otherwise, return None.

This is equivalent to:

option match {
 case Some(x) if p(x) => Some(x)
 case _               => None
}

Source@inline

final def filterNot(p: A => Boolean): Option[A]

Returns this scala.Option if it is nonempty and applying the predicate p to this scala.Option's value returns false. Otherwise, return None.

This is equivalent to:

option match {
 case Some(x) if !p(x) => Some(x)
 case _                => None
}

Source@inline

final def flatMap[B](f: A => Option[B]): Option[B]

Returns the result of applying f to this scala.Option's value if this scala.Option is nonempty. Returns None if this scala.Option is empty. Slightly different from map in that f is expected to return an scala.Option (which could be None).

This is equivalent to:

option match {
 case Some(x) => f(x)
 case None    => None
}

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def flatten[B](implicit ev: A <:< Option[B]): Option[B]

Returns the nested scala.Option value if it is nonempty. Otherwise, return None.

This is equivalent to:

option match {
 case Some(Some(b)) => Some(b)
 case _             => None
}

Some(Some("something")).flatten

Source@inline

final def fold[B](ifEmpty: => B)(f: A => B): B

Returns the result of applying f to this scala.Option's value if the scala.Option is nonempty. Otherwise, evaluates expression ifEmpty.

This is equivalent to:

option match {
 case Some(x) => f(x)
 case None    => ifEmpty
}

This is also equivalent to:

option map f getOrElse ifEmpty

Source@inline

final def forall(p: A => Boolean): Boolean

Returns true if this option is empty or the predicate p returns true when applied to this scala.Option's value.

This is equivalent to:

option match {
 case Some(x) => p(x)
 case None    => true
}

Source@inline

final def foreach[U](f: A => U): Unit

Apply the given procedure f to the option's value, if it is nonempty. Otherwise, do nothing.

This is equivalent to:

option match {
 case Some(x) => f(x)
 case None    => ()
}

Source@inline

final def getOrElse[B >: A](default: => B): B

Returns the option's value if the option is nonempty, otherwise return the result of evaluating default.

This is equivalent to:

option match {
 case Some(x) => x
 case None    => default
}

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final def isDefined: Boolean

Returns true if the option is an instance of scala.Some, false otherwise.

This is equivalent to:

option match {
 case Some(_) => true
 case None    => false
}

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final def isEmpty: Boolean

Returns true if the option is None, false otherwise.

This is equivalent to:

option match {
 case Some(_) => false
 case None    => true
}

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def iterableFactory: IterableFactory[Iterable]

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def iterator: Iterator[A]

Returns a singleton iterator returning the scala.Option's value if it is nonempty, or an empty iterator if the option is empty.

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final override def knownSize: Int

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def lazyZip[B](that: Iterable[B]): LazyZip2[A, B, Iterable[A]]

Analogous to zip except that the elements in each collection are not consumed until a strict operation is invoked on the returned LazyZip2 decorator.

Calls to lazyZip can be chained to support higher arities (up to 4) without incurring the expense of constructing and deconstructing intermediary tuples.

val xs = List(1, 2, 3)
val res = (xs lazyZip xs lazyZip xs lazyZip xs).map((a, b, c, d) => a + b + c + d)
// res == List(4, 8, 12)

Source@inline

final def map[B](f: A => B): Option[B]

Returns a scala.Some containing the result of applying f to this scala.Option's value if this scala.Option is nonempty. Otherwise return None.

This is equivalent to:

option match {
 case Some(x) => Some(f(x))
 case None    => None
}

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final def nonEmpty: Boolean

Returns false if the option is None, true otherwise.

This is equivalent to:

option match {
 case Some(_) => true
 case None    => false
}

Source@inline

final def orElse[B >: A](alternative: => Option[B]): Option[B]

Returns this scala.Option if it is nonempty, otherwise return the result of evaluating alternative.

This is equivalent to:

option match {
 case Some(x) => Some(x)
 case None    => alternative
}

Source@inline

final def orNull[A1 >: A](implicit ev: Null <:< A1): A1

Returns the option's value if it is nonempty, or null if it is empty.

Although the use of null is discouraged, code written to use scala.Option must often interface with code that expects and returns nulls.

This is equivalent to:

option match {
 case Some(x) => x
 case None    => null
}

val initialText: Option[String] = getInitialText
val textField = new JComponent(initialText.orNull,20)

Source@inline

final def toLeft[X](right: => X): Either[A, X]

Returns a scala.util.Right containing the given argument right if this is empty, or a scala.util.Left containing this scala.Option's value if this scala.Option is nonempty.

This is equivalent to:

option match {
 case Some(x) => Left(x)
 case None    => Right(right)
}

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def toList: List[A]

Returns a singleton list containing the scala.Option's value if it is nonempty, or the empty list if the scala.Option is empty.

This is equivalent to:

option match {
 case Some(x) => List(x)
 case None    => Nil
}

Source@inline

final def toRight[X](left: => X): Either[X, A]

Returns a scala.util.Left containing the given argument left if this scala.Option is empty, or a scala.util.Right containing this scala.Option's value if this is nonempty.

This is equivalent to:

option match {
 case Some(x) => Right(x)
 case None    => Left(left)
}

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final def unzip[A1, A2](implicit asPair: A <:< (A1, A2)): (Option[A1], Option[A2])

Converts an Option of a pair into an Option of the first element and an Option of the second element.

This is equivalent to:

option match {
  case Some((x, y)) => (Some(x), Some(y))
  case _            => (None,    None)
}

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final def unzip3[A1, A2, A3](implicit asTriple: A <:< (A1, A2, A3)): (Option[A1], Option[A2], Option[A3])

Converts an Option of a triple into three Options, one containing the element from each position of the triple.

This is equivalent to:

option match {
  case Some((x, y, z)) => (Some(x), Some(y), Some(z))
  case _               => (None,    None,    None)
}

Source@inline

final def withFilter(p: A => Boolean): WithFilter

Necessary to keep scala.Option from being implicitly converted to scala.collection.Iterable in for comprehensions.

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final def zip[A1 >: A, B](that: Option[B]): Option[(A1, B)]

Returns a scala.Some formed from this option and another option by combining the corresponding elements in a pair. If either of the two options is empty, None is returned.

This is equivalent to:

(option1, option2) match {
  case (Some(x), Some(y)) => Some((x, y))
  case _                  => None
}

// Returns Some(("foo", "bar")) because both options are nonempty.
Some("foo") zip Some("bar")
// Returns None because `that` option is empty.
Some("foo") zip None
// Returns None because `this` option is empty.
None zip Some("bar")

Inherited methods

Source@inline

final def ++[B >: A](suffix: IterableOnce[B]): Iterable[B]

Alias for concat

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final def addString(b: StringBuilder): StringBuilder

Appends all elements of this collection to a string builder. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection without any separator string.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> val h = a.addString(b)
h: StringBuilder = 1234

Source@inline

final def addString(b: StringBuilder, sep: String): StringBuilder

Appends all elements of this collection to a string builder using a separator string. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection, separated by the string sep.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> a.addString(b, ", ")
res0: StringBuilder = 1, 2, 3, 4

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def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder

Appends all elements of this collection to a string builder using start, end, and separator strings. The written text begins with the string start and ends with the string end. Inside, the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> a.addString(b , "List(" , ", " , ")")
res5: StringBuilder = List(1, 2, 3, 4)

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def canEqual(that: Any): Boolean

A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

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def collect[B](pf: PartialFunction[A, B]): Iterable[B]

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def collectFirst[B](pf: PartialFunction[A, B]): Option[B]

Finds the first element of the collection for which the given partial function is defined, and applies the partial function to it.

Note: may not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def concat[B >: A](suffix: IterableOnce[B]): Iterable[B]

Returns a new iterable collection containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the iterable collection is the most specific superclass encompassing the element types of the two operands.

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def copyToArray[B >: A](xs: Array[B], start: Int, len: Int): Int

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with at most len elements of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached, or len elements have been copied.

Source@deprecatedOverriding("This should always forward to the 3-arg version of this method", since = "2.13.4")

def copyToArray[B >: A](xs: Array[B], start: Int): Int

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.

Source@deprecatedOverriding("This should always forward to the 3-arg version of this method", since = "2.13.4")

def copyToArray[B >: A](xs: Array[B]): Int

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.

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def corresponds[B](that: IterableOnce[B])(p: (A, B) => Boolean): Boolean

Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.

Note: will not terminate for infinite-sized collections.

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def count(p: A => Boolean): Int

Counts the number of elements in the collection which satisfy a predicate.

Note: will not terminate for infinite-sized collections.

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def drop(n: Int): Iterable[A]

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def dropRight(n: Int): Iterable[A]

Selects all elements except last n ones.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def dropWhile(p: A => Boolean): Iterable[A]

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def exists(p: A => Boolean): Boolean

Tests whether a predicate holds for at least one element of this collection.

Note: may not terminate for infinite-sized collections.

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def filter(pred: A => Boolean): Iterable[A]

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def filterNot(pred: A => Boolean): Iterable[A]

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def find(p: A => Boolean): Option[A]

Finds the first element of the collection satisfying a predicate, if any.

Note: may not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def flatMap[B](f: A => IterableOnce[B]): Iterable[B]

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def flatten[B](implicit asIterable: A => IterableOnce[B]): Iterable[B]

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def fold[A1 >: A](z: A1)(op: (A1, A1) => A1): A1

Folds the elements of this collection using the specified associative binary operator. The default implementation in IterableOnce is equivalent to foldLeft but may be overridden for more efficient traversal orders.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

Note: will not terminate for infinite-sized collections.

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def foldLeft[B](z: B)(op: (B, A) => B): B

Applies a binary operator to a start value and all elements of this collection, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

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def foldRight[B](z: B)(op: (A, B) => B): B

Applies a binary operator to all elements of this collection and a start value, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

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def forall(p: A => Boolean): Boolean

Tests whether a predicate holds for all elements of this collection.

Note: may not terminate for infinite-sized collections.

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def foreach[U](f: A => U): Unit

Apply f to each element for its side effects Note: [U] parameter needed to help scalac's type inference.

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protected def fromSpecific(coll: IterableOnce[A]): Iterable[A]

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def groupBy[K](f: A => K): Map[K, Iterable[A]]

Partitions this iterable collection into a map of iterable collections according to some discriminator function.

Note: Even when applied to a view or a lazy collection it will always force the elements.

(xs groupBy f)(k) = xs filter (x => f(x) == k)

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def groupMap[K, B](key: A => K)(f: A => B): Map[K, Iterable[B]]

Partitions this iterable collection into a map of iterable collections according to a discriminator function key. Each element in a group is transformed into a value of type B using the value function.

It is equivalent to groupBy(key).mapValues(_.map(f)), but more efficient.

case class User(name: String, age: Int)

def namesByAge(users: Seq[User]): Map[Int, Seq[String]] =
  users.groupMap(_.age)(_.name)

Note: Even when applied to a view or a lazy collection it will always force the elements.

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def groupMapReduce[K, B](key: A => K)(f: A => B)(reduce: (B, B) => B): Map[K, B]

Partitions this iterable collection into a map according to a discriminator function key. All the values that have the same discriminator are then transformed by the f function and then reduced into a single value with the reduce function.

It is equivalent to groupBy(key).mapValues(_.map(f).reduce(reduce)), but more efficient.

def occurrences[A](as: Seq[A]): Map[A, Int] =
  as.groupMapReduce(identity)(_ => 1)(_ + _)

Note: Even when applied to a view or a lazy collection it will always force the elements.

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def grouped(size: Int): Iterator[Iterable[A]]

Partitions elements in fixed size iterable collections.

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def head: A

Selects the first element of this iterable collection.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def headOption: Option[A]

Optionally selects the first element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def init: Iterable[A]

The initial part of the collection without its last element.

Note: Even when applied to a view or a lazy collection it will always force the elements.

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def inits: Iterator[Iterable[A]]

Iterates over the inits of this iterable collection. The first value will be this iterable collection and the final one will be an empty iterable collection, with the intervening values the results of successive applications of init.

Note: Even when applied to a view or a lazy collection it will always force the elements.

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def isEmpty: Boolean

Tests whether the collection is empty.

Note: Implementations in subclasses that are not repeatedly traversable must take care not to consume any elements when isEmpty is called.

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def iterator: Iterator[A]

Iterator can be used only once

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def knownSize: Int

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def last: A

Selects the last element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def lastOption: Option[A]

Optionally selects the last element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def map[B](f: A => B): Iterable[B]

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def max[B >: A](implicit ord: Ordering[B]): A

Finds the largest element.

Note: will not terminate for infinite-sized collections.

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def maxBy[B](f: A => B)(implicit cmp: Ordering[B]): A

Finds the first element which yields the largest value measured by function f.

Note: will not terminate for infinite-sized collections.

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def maxByOption[B](f: A => B)(implicit cmp: Ordering[B]): Option[A]

Finds the first element which yields the largest value measured by function f.

Note: will not terminate for infinite-sized collections.

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def maxOption[B >: A](implicit ord: Ordering[B]): Option[A]

Finds the largest element.

Note: will not terminate for infinite-sized collections.

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def min[B >: A](implicit ord: Ordering[B]): A

Finds the smallest element.

Note: will not terminate for infinite-sized collections.

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def minBy[B](f: A => B)(implicit cmp: Ordering[B]): A

Finds the first element which yields the smallest value measured by function f.

Note: will not terminate for infinite-sized collections.

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def minByOption[B](f: A => B)(implicit cmp: Ordering[B]): Option[A]

Finds the first element which yields the smallest value measured by function f.

Note: will not terminate for infinite-sized collections.

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def minOption[B >: A](implicit ord: Ordering[B]): Option[A]

Finds the smallest element.

Note: will not terminate for infinite-sized collections.

Source@inline

final def mkString: String

Displays all elements of this collection in a string.

Delegates to addString, which can be overridden.

Source@inline

final def mkString(sep: String): String

Displays all elements of this collection in a string using a separator string.

Delegates to addString, which can be overridden.

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final def mkString(start: String, sep: String, end: String): String

Displays all elements of this collection in a string using start, end, and separator strings.

Delegates to addString, which can be overridden.

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protected def newSpecificBuilder: Builder[A, Iterable[A]]

Source@deprecatedOverriding("nonEmpty is defined as !isEmpty; override isEmpty instead", "2.13.0")

def nonEmpty: Boolean

Tests whether the collection is not empty.

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def partition(p: A => Boolean): (Iterable[A], Iterable[A])

A pair of, first, all elements that satisfy predicate p and, second, all elements that do not. Interesting because it splits a collection in two.

The default implementation provided here needs to traverse the collection twice. Strict collections have an overridden version of partition in StrictOptimizedIterableOps, which requires only a single traversal.

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def partitionMap[A1, A2](f: A => Either[A1, A2]): (Iterable[A1], Iterable[A2])

Applies a function f to each element of the iterable collection and returns a pair of iterable collections: the first one made of those values returned by f that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.

Example:

val xs = Iterable(1, "one", 2, "two", 3, "three") partitionMap {
 case i: Int => Left(i)
 case s: String => Right(s)
}
// xs == (Iterable(1, 2, 3),
//        Iterable(one, two, three))

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def product[B >: A](implicit num: Numeric[B]): B

Multiplies up the elements of this collection.

Note: will not terminate for infinite-sized collections.

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def productArity: Int

The size of this product.

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def productElement(n: Int): Any

The nth element of this product, 0-based. In other words, for a product A(x1, ..., xk), returns x(n+1) where 0 <= n < k.

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def productElementName(n: Int): String

The name of the nth element of this product, 0-based. In the default implementation, an empty string.

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def productElementNames: Iterator[String]

An iterator over the names of all the elements of this product.

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def productIterator: Iterator[Any]

An iterator over all the elements of this product.

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def productPrefix: String

A string used in the toString methods of derived classes. Implementations may override this method to prepend a string prefix to the result of toString methods.

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def reduce[B >: A](op: (B, B) => B): B

Reduces the elements of this collection using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

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def reduceLeft[B >: A](op: (B, A) => B): B

Applies a binary operator to all elements of this collection, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

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def reduceLeftOption[B >: A](op: (B, A) => B): Option[B]

Optionally applies a binary operator to all elements of this collection, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

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def reduceOption[B >: A](op: (B, B) => B): Option[B]

Reduces the elements of this collection, if any, using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

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def reduceRight[B >: A](op: (A, B) => B): B

Applies a binary operator to all elements of this collection, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

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def reduceRightOption[B >: A](op: (A, B) => B): Option[B]

Optionally applies a binary operator to all elements of this collection, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

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protected def reversed: Iterable[A]

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def scan[B >: A](z: B)(op: (B, B) => B): Iterable[B]

Computes a prefix scan of the elements of the collection.

Note: The neutral element z may be applied more than once.

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def scanLeft[B](z: B)(op: (B, A) => B): Iterable[B]

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def scanRight[B](z: B)(op: (A, B) => B): Iterable[B]

Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Example:

List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)

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def size: Int

The size of this collection.

Note: will not terminate for infinite-sized collections.

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def sizeCompare(that: Iterable[_]): Int

Compares the size of this iterable collection to the size of another Iterable.

x <  0       if this.size <  that.size
x == 0       if this.size == that.size
x >  0       if this.size >  that.size

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def sizeCompare(otherSize: Int): Int

Compares the size of this iterable collection to a test value.

x <  0       if this.size <  otherSize
x == 0       if this.size == otherSize
x >  0       if this.size >  otherSize

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final def sizeIs: SizeCompareOps

Returns a value class containing operations for comparing the size of this iterable collection to a test value.

These operations are implemented in terms of sizeCompare(Int), and allow the following more readable usages:

this.sizeIs < size     // this.sizeCompare(size) < 0
this.sizeIs <= size    // this.sizeCompare(size) <= 0
this.sizeIs == size    // this.sizeCompare(size) == 0
this.sizeIs != size    // this.sizeCompare(size) != 0
this.sizeIs >= size    // this.sizeCompare(size) >= 0
this.sizeIs > size     // this.sizeCompare(size) > 0

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def slice(from: Int, until: Int): Iterable[A]

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def sliding(size: Int, step: Int): Iterator[Iterable[A]]

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

The returned iterator will be empty when called on an empty collection. The last element the iterator produces may be smaller than the window size when the original collection isn't exhausted by the window before it and its last element isn't skipped by the step before it.

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def sliding(size: Int): Iterator[Iterable[A]]

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

An empty collection returns an empty iterator, and a non-empty collection containing fewer elements than the window size returns an iterator that will produce the original collection as its only element.

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def span(p: A => Boolean): (Iterable[A], Iterable[A])

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def stepper[S <: Stepper[_]](implicit shape: StepperShape[A, S]): S

Returns a scala.collection.Stepper for the elements of this collection.

The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.

The implicit scala.collection.StepperShape parameter defines the resulting Stepper type according to the element type of this collection.

• For collections of Int, Short, Byte or Char, an scala.collection.IntStepper is returned

• For collections of Double or Float, a scala.collection.DoubleStepper is returned

• For collections of Long a scala.collection.LongStepper is returned

• For any other element type, an scala.collection.AnyStepper is returned

Note that this method is overridden in subclasses and the return type is refined to S with EfficientSplit, for example scala.collection.IndexedSeqOps.stepper. For Steppers marked with scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters allow creating parallel streams, whereas bare Steppers can be converted only to sequential streams.

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def stepper[S <: Stepper[_]](implicit shape: StepperShape[A, S]): S

Returns a scala.collection.Stepper for the elements of this collection.

The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.

The implicit scala.collection.StepperShape parameter defines the resulting Stepper type according to the element type of this collection.

• For collections of Int, Short, Byte or Char, an scala.collection.IntStepper is returned

• For collections of Double or Float, a scala.collection.DoubleStepper is returned

• For collections of Long a scala.collection.LongStepper is returned

• For any other element type, an scala.collection.AnyStepper is returned

Note that this method is overridden in subclasses and the return type is refined to S with EfficientSplit, for example scala.collection.IndexedSeqOps.stepper. For Steppers marked with scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters allow creating parallel streams, whereas bare Steppers can be converted only to sequential streams.

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def sum[B >: A](implicit num: Numeric[B]): B

Sums up the elements of this collection.

Note: will not terminate for infinite-sized collections.

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def tail: Iterable[A]

The rest of the collection without its first element.

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def tails: Iterator[Iterable[A]]

Iterates over the tails of this iterable collection. The first value will be this iterable collection and the final one will be an empty iterable collection, with the intervening values the results of successive applications of tail.

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def take(n: Int): Iterable[A]

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def takeRight(n: Int): Iterable[A]

Selects the last n elements.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def takeWhile(p: A => Boolean): Iterable[A]

Takes longest prefix of elements that satisfy a predicate.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def to[C1](factory: Factory[A, C1]): C1

Given a collection factory factory, convert this collection to the appropriate representation for the current element type A. Example uses:

xs.to(List) xs.to(ArrayBuffer) xs.to(BitSet) // for xs: Iterable[Int]

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def toArray[B >: A : ClassTag]: Array[B]

Convert collection to array.

Implementation note: DO NOT call Array.from from this method.

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final def toBuffer[B >: A]: Buffer[B]

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def toIndexedSeq: IndexedSeq[A]

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def toList: List[A]

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def toMap[K, V](implicit ev: A <:< (K, V)): Map[K, V]

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def toSeq: Seq[A]

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def toSet[B >: A]: Set[B]

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def toVector: Vector[A]

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def transpose[B](implicit asIterable: A => Iterable[B]): Iterable[Iterable[B]]

Transposes this iterable collection of iterable collections into a iterable collection of iterable collections.

The resulting collection's type will be guided by the static type of iterable collection. For example:

val xs = List(
           Set(1, 2, 3),
           Set(4, 5, 6)).transpose
// xs == List(
//         List(1, 4),
//         List(2, 5),
//         List(3, 6))

val ys = Vector(
           List(1, 2, 3),
           List(4, 5, 6)).transpose
// ys == Vector(
//         Vector(1, 4),
//         Vector(2, 5),
//         Vector(3, 6))

Note: Even when applied to a view or a lazy collection it will always force the elements.

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def unzip[A1, A2](implicit asPair: A => (A1, A2)): (Iterable[A1], Iterable[A2])

Converts this iterable collection of pairs into two collections of the first and second half of each pair.

val xs = Iterable(
           (1, "one"),
           (2, "two"),
           (3, "three")).unzip
// xs == (Iterable(1, 2, 3),
//        Iterable(one, two, three))

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def unzip3[A1, A2, A3](implicit asTriple: A => (A1, A2, A3)): (Iterable[A1], Iterable[A2], Iterable[A3])

Converts this iterable collection of triples into three collections of the first, second, and third element of each triple.

val xs = Iterable(
           (1, "one", '1'),
           (2, "two", '2'),
           (3, "three", '3')).unzip3
// xs == (Iterable(1, 2, 3),
//        Iterable(one, two, three),
//        Iterable(1, 2, 3))

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def view: View[A]

A view over the elements of this collection.

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def withFilter(p: A => Boolean): WithFilter[A, Iterable]

Creates a non-strict filter of this iterable collection.

Note: the difference between c filter p and c withFilter p is that the former creates a new collection, whereas the latter only restricts the domain of subsequent map, flatMap, foreach, and withFilter operations.

Note: might return different results for different runs, unless the underlying collection type is ordered.

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def zip[B](that: IterableOnce[B]): Iterable[(A, B)]

Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs. If one of the two collections is longer than the other, its remaining elements are ignored.

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def zipAll[A1 >: A, B](that: Iterable[B], thisElem: A1, thatElem: B): Iterable[(A1, B)]

Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.

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def zipWithIndex: Iterable[(A, Int)]