sbt/util/collection/Attributes.scala

/* sbt -- Simple Build Tool
 * Copyright 2010 Mark Harrah
 */
package sbt

import Types._

// T must be invariant to work properly.
//  Because it is sealed and the only instances go through make,
//  a single AttributeKey instance cannot conform to AttributeKey[T] for different Ts
sealed trait AttributeKey[T] {
	def label: String
}
object AttributeKey
{
	def apply[T](name: String): AttributeKey[T] = new AttributeKey[T] { def label = name }
}

trait AttributeMap
{
	def apply[T](k: AttributeKey[T]): T
	def get[T](k: AttributeKey[T]): Option[T]
	def contains[T](k: AttributeKey[T]): Boolean
	def put[T](k: AttributeKey[T], value: T): AttributeMap
	def keys: Iterable[AttributeKey[_]]
	def ++(o: AttributeMap): AttributeMap
	def entries: Iterable[AttributeEntry[_]]
	def isEmpty: Boolean
}
object AttributeMap
{
	val empty: AttributeMap = new BasicAttributeMap(Map.empty)
}
private class BasicAttributeMap(private val backing: Map[AttributeKey[_], Any]) extends AttributeMap
{
	def isEmpty: Boolean = backing.isEmpty
	def apply[T](k: AttributeKey[T]) = backing(k).asInstanceOf[T]
	def get[T](k: AttributeKey[T]) = backing.get(k).asInstanceOf[Option[T]]
	def contains[T](k: AttributeKey[T]) = backing.contains(k)
	def put[T](k: AttributeKey[T], value: T): AttributeMap = new BasicAttributeMap( backing.updated(k, value) )
	def keys: Iterable[AttributeKey[_]] = backing.keys
	def ++(o: AttributeMap): AttributeMap =
		o match {
			case bam: BasicAttributeMap => new BasicAttributeMap(backing ++ bam.backing)
			case _ => o ++ this
		}
	def entries: Iterable[AttributeEntry[_]] =
		for( (k: AttributeKey[kt], v) <- backing) yield AttributeEntry(k, v.asInstanceOf[kt])
	override def toString = entries.mkString("(", ", ", ")")
}

// type inference required less generality
final case class AttributeEntry[T](a: AttributeKey[T], b: T)
{
	override def toString = a.label + ": " + b
}

final case class Attributed[D](data: D)(val metadata: AttributeMap)
{
	def put[T](key: AttributeKey[T], value: T): Attributed[D] = Attributed(data)(metadata.put(key, value))
}
object Attributed
{
	implicit def blank[T](data: T): Attributed[T] = Attributed(data)(AttributeMap.empty)
}