sbt.Relation.scala Maven / Gradle / Ivy
/* sbt -- Simple Build Tool
* Copyright 2010 Mark Harrah
*/
package sbt
import Relation._
object Relation
{
/** Constructs a new immutable, finite relation that is initially empty. */
def empty[A,B]: Relation[A,B] = make(Map.empty, Map.empty)
/** Constructs a [[Relation]] from underlying `forward` and `reverse` representations, without checking that they are consistent.
* This is a low-level constructor and the alternatives [[empty]] and [[reconstruct]] should be preferred. */
def make[A,B](forward: Map[A,Set[B]], reverse: Map[B, Set[A]]): Relation[A,B] = new MRelation(forward, reverse)
/** Constructs a relation such that for every entry `_1 -> _2s` in `forward` and every `_2` in `_2s`, `(_1, _2)` is in the relation. */
def reconstruct[A,B](forward: Map[A, Set[B]]): Relation[A,B] =
{
val reversePairs = for( (a,bs) <- forward.view; b <- bs.view) yield (b, a)
val reverse = (Map.empty[B,Set[A]] /: reversePairs) { case (m, (b, a)) => add(m, b, a :: Nil) }
make(forward filter { case (a, bs) => bs.nonEmpty }, reverse)
}
def merge[A,B](rels: Traversable[Relation[A,B]]): Relation[A,B] = (Relation.empty[A, B] /: rels)(_ ++ _)
private[sbt] def remove[X,Y](map: M[X,Y], from: X, to: Y): M[X,Y] =
map.get(from) match {
case Some(tos) =>
val newSet = tos - to
if(newSet.isEmpty) map - from else map.updated(from, newSet)
case None => map
}
private[sbt] def combine[X,Y](a: M[X,Y], b: M[X,Y]): M[X,Y] =
(a /: b) { (map, mapping) => add(map, mapping._1, mapping._2) }
private[sbt] def add[X,Y](map: M[X,Y], from: X, to: Traversable[Y]): M[X,Y] =
map.updated(from, get(map, from) ++ to)
private[sbt] def get[X,Y](map: M[X,Y], t: X): Set[Y] = map.getOrElse(t, Set.empty[Y])
private[sbt] type M[X,Y] = Map[X, Set[Y]]
}
/** Binary relation between A and B. It is a set of pairs (_1, _2) for _1 in A, _2 in B. */
trait Relation[A,B]
{
/** Returns the set of all `_2`s such that `(_1, _2)` is in this relation. */
def forward(_1: A): Set[B]
/** Returns the set of all `_1`s such that `(_1, _2)` is in this relation. */
def reverse(_2: B): Set[A]
/** Includes `pair` in the relation. */
def +(pair: (A, B)): Relation[A,B]
/** Includes `(a, b)` in the relation. */
def +(a: A, b: B): Relation[A,B]
/** Includes in the relation `(a, b)` for all `b` in `bs`. */
def +(a: A, bs: Traversable[B]): Relation[A,B]
/** Returns the union of the relation `r` with this relation. */
def ++(r: Relation[A,B]): Relation[A,B]
/** Includes the given pairs in this relation. */
def ++(rs: Traversable[(A,B)]): Relation[A,B]
/** Removes all elements `(_1, _2)` for all `_1` in `_1s` from this relation. */
def --(_1s: Traversable[A]): Relation[A,B]
/** Removes all `pairs` from this relation. */
def --(pairs: TraversableOnce[(A,B)]): Relation[A,B]
/** Removes all `relations` from this relation. */
def --(relations: Relation[A,B]): Relation[A,B]
/** Removes all pairs `(_1, _2)` from this relation. */
def -(_1: A): Relation[A,B]
/** Removes `pair` from this relation. */
def -(pair: (A,B)): Relation[A,B]
/** Returns the set of all `_1`s such that `(_1, _2)` is in this relation. */
def _1s: collection.Set[A]
/** Returns the set of all `_2`s such that `(_1, _2)` is in this relation. */
def _2s: collection.Set[B]
/** Returns the number of pairs in this relation */
def size: Int
/** Returns true iff `(a,b)` is in this relation*/
def contains(a: A, b: B): Boolean
/** Returns a relation with only pairs `(a,b)` for which `f(a,b)` is true.*/
def filter(f: (A,B) => Boolean): Relation[A,B]
/** Returns a pair of relations: the first contains only pairs `(a,b)` for which `f(a,b)` is true and
* the other only pairs `(a,b)` for which `f(a,b)` is false. */
def partition(f: (A,B) => Boolean): (Relation[A,B], Relation[A,B])
/** Partitions this relation into a map of relations according to some discriminator function. */
def groupBy[K](discriminator: ((A,B)) => K): Map[K, Relation[A,B]]
/** Returns all pairs in this relation.*/
def all: Traversable[(A,B)]
/** Represents this relation as a `Map` from a `_1` to the set of `_2`s such that `(_1, _2)` is in this relation.
*
* Specifically, there is one entry for each `_1` such that `(_1, _2)` is in this relation for some `_2`.
* The value associated with a given `_1` is the set of all `_2`s such that `(_1, _2)` is in this relation.*/
def forwardMap: Map[A, Set[B]]
/** Represents this relation as a `Map` from a `_2` to the set of `_1`s such that `(_1, _2)` is in this relation.
*
* Specifically, there is one entry for each `_2` such that `(_1, _2)` is in this relation for some `_1`.
* The value associated with a given `_2` is the set of all `_1`s such that `(_1, _2)` is in this relation.*/
def reverseMap: Map[B, Set[A]]
}
// Note that we assume without checking that fwd and rev are consistent.
private final class MRelation[A,B](fwd: Map[A, Set[B]], rev: Map[B, Set[A]]) extends Relation[A,B]
{
def forwardMap = fwd
def reverseMap = rev
def forward(t: A) = get(fwd, t)
def reverse(t: B) = get(rev, t)
def _1s = fwd.keySet
def _2s = rev.keySet
def size = (fwd.valuesIterator map { _.size }).foldLeft(0)(_ + _)
def all: Traversable[(A,B)] = fwd.iterator.flatMap { case (a, bs) => bs.iterator.map( b => (a,b) ) }.toTraversable
def +(pair: (A,B)) = this + (pair._1, Set(pair._2))
def +(from: A, to: B) = this + (from, to :: Nil)
def +(from: A, to: Traversable[B]) = if(to.isEmpty) this else
new MRelation( add(fwd, from, to), (rev /: to) { (map, t) => add(map, t, from :: Nil) })
def ++(rs: Traversable[(A,B)]) = ((this: Relation[A,B]) /: rs) { _ + _ }
def ++(other: Relation[A,B]) = new MRelation[A,B]( combine(fwd, other.forwardMap), combine(rev, other.reverseMap) )
def --(ts: Traversable[A]): Relation[A,B] = ((this: Relation[A,B]) /: ts) { _ - _ }
def --(pairs: TraversableOnce[(A,B)]): Relation[A,B] = ((this: Relation[A,B]) /: pairs) { _ - _ }
def --(relations: Relation[A,B]): Relation[A,B] = --(relations.all)
def -(pair: (A,B)): Relation[A,B] =
new MRelation( remove(fwd, pair._1, pair._2), remove(rev, pair._2, pair._1) )
def -(t: A): Relation[A,B] =
fwd.get(t) match {
case Some(rs) =>
val upRev = (rev /: rs) { (map, r) => remove(map, r, t) }
new MRelation(fwd - t, upRev)
case None => this
}
def filter(f: (A,B) => Boolean): Relation[A,B] = Relation.empty[A,B] ++ all.filter(f.tupled)
def partition(f: (A,B) => Boolean): (Relation[A,B], Relation[A,B]) = {
val (y, n) = all.partition(f.tupled)
(Relation.empty[A,B] ++ y, Relation.empty[A,B] ++ n)
}
def groupBy[K](discriminator: ((A,B)) => K): Map[K, Relation[A,B]] = all.groupBy(discriminator) mapValues { Relation.empty[A,B] ++ _ }
def contains(a: A, b: B): Boolean = forward(a)(b)
override def equals(other: Any) = other match {
// We assume that the forward and reverse maps are consistent, so we only use the forward map
// for equality. Note that key -> Empty is semantically the same as key not existing.
case o: MRelation[A,B] => forwardMap.filterNot(_._2.isEmpty) == o.forwardMap.filterNot(_._2.isEmpty)
case _ => false
}
override def hashCode = fwd.filterNot(_._2.isEmpty).hashCode()
override def toString = all.map { case (a,b) => a + " -> " + b }.mkString("Relation [", ", ", "]")
}
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