scala.collection.mutable.Builder.scala Maven / Gradle / Ivy
The newest version!
/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala.collection.mutable
/** Base trait for collection builders.
*
* After calling `result()` the behavior of a Builder (which is not also a [[scala.collection.mutable.ReusableBuilder]])
* is undefined. No further methods should be called. It is common for mutable collections to be their own non-reusable
* Builder, in which case `result()` simply returns `this`.
*
* @see [[scala.collection.mutable.ReusableBuilder]] for Builders which can be reused after calling `result()`
*/
trait Builder[-A, +To] extends Growable[A] { self =>
/** Clears the contents of this builder.
* After execution of this method the builder will contain no elements.
*/
def clear(): Unit
/** Result collection consisting of all elements appended so far. */
def result(): To
/** Gives a hint how many elements are expected to be added in total
* by the time `result` is called.
*
* Some builder classes will optimize their representation based on the hint.
* However, builder implementations are required to work correctly even if the hint is
* wrong, e.g., a different number of elements is added, or the hint is out of range.
*
* The default implementation simply ignores the hint.
*
* @param size the hint how many elements will be added.
*/
def sizeHint(size: Int): Unit = ()
/** Gives a hint that the `result` of this builder is expected
* to have the same size as the given collection, plus some delta.
*
* This method provides a hint only if the collection has a known size,
* as specified by the following pseudocode:
*
* {{{
* if (coll.knownSize != -1)
* if (coll.knownSize + delta <= 0) sizeHint(0)
* else sizeHint(coll.knownSize + delta)
* }}}
*
* If the delta is negative and the result size is known to be negative,
* then the size hint is issued at zero.
*
* Some builder classes will optimize their representation based on the hint.
* However, builder implementations are required to work correctly even if the hint is
* wrong, i.e., if a different number of elements is added.
*
* @param coll the collection which serves as a hint for the result's size.
* @param delta a correction to add to the `coll.size` to produce the size hint (zero if omitted).
*/
final def sizeHint(coll: scala.collection.IterableOnce[_], delta: Int = 0): Unit =
coll.knownSize match {
case -1 =>
case sz => sizeHint(0 max sz + delta)
}
/** Gives a hint how many elements are expected to be added
* when the next `result` is called, together with an upper bound
* given by the size of some other collection. Some builder classes
* will optimize their representation based on the hint. However,
* builder implementations are still required to work correctly even if the hint is
* wrong, i.e. a different number of elements is added.
*
* @param size the hint how many elements will be added.
* @param boundingColl the bounding collection. If it is
* an IndexedSeqLike, then sizes larger
* than collection's size are reduced.
*/
// should probably be `boundingColl: IterableOnce[_]`, but binary compatibility
final def sizeHintBounded(size: Int, boundingColl: scala.collection.Iterable[_]): Unit = {
val s = boundingColl.knownSize
if (s != -1) {
sizeHint(scala.math.min(s, size))
}
}
/** A builder resulting from this builder by mapping the result using `f`. */
def mapResult[NewTo](f: To => NewTo): Builder[A, NewTo] = new Builder[A, NewTo] {
def addOne(x: A): this.type = { self += x; this }
def clear(): Unit = self.clear()
override def addAll(xs: IterableOnce[A]): this.type = { self ++= xs; this }
override def sizeHint(size: Int): Unit = self.sizeHint(size)
def result(): NewTo = f(self.result())
override def knownSize: Int = self.knownSize
}
}