ich in der scala Bibliothek spähte und es scheint, dass die einzigen Verweise auf diese vier spezifischen impl von Karte in ihrer eigenen sind "aktualisiert" und "-" Methoden. Die Magie beginnt in MutableMapFactory in der Methode newBuilder, in der Map.empty aufgerufen wird, die die EmptyMap-Klasse erzeugt. Dann Aufruf aktualisiert und Hinzufügen von Schlüssel und Wert macht es Map1. Wenn Sie dann die aktualisierte Methode in Map1 erneut aufrufen, kann entweder Map1 oder Map2 und Aufrufmethode zu EmptyMap führen. etc ...
private object EmptyMap extends AbstractMap[Any, Nothing] with Map[Any, Nothing] with Serializable {
override def size: Int = 0
def get(key: Any): Option[Nothing] = None
def iterator: Iterator[(Any, Nothing)] = Iterator.empty
override def updated [B1] (key: Any, value: B1): Map[Any, B1] = new Map1(key, value)
def + [B1](kv: (Any, B1)): Map[Any, B1] = updated(kv._1, kv._2)
def - (key: Any): Map[Any, Nothing] = this
}
class Map1[A, +B](key1: A, value1: B) extends AbstractMap[A, B] with Map[A, B] with Serializable {
override def size = 1
def get(key: A): Option[B] =
if (key == key1) Some(value1) else None
def iterator = Iterator((key1, value1))
override def updated [B1 >: B] (key: A, value: B1): Map[A, B1] =
if (key == key1) new Map1(key1, value)
else new Map2(key1, value1, key, value)
def + [B1 >: B](kv: (A, B1)): Map[A, B1] = updated(kv._1, kv._2)
def - (key: A): Map[A, B] =
if (key == key1) Map.empty else this
override def foreach[U](f: ((A, B)) => U): Unit = {
f((key1, value1))
}
}
class Map2[A, +B](key1: A, value1: B, key2: A, value2: B) extends AbstractMap[A, B] with Map[A, B] with Serializable {
override def size = 2
def get(key: A): Option[B] =
if (key == key1) Some(value1)
else if (key == key2) Some(value2)
else None
def iterator = Iterator((key1, value1), (key2, value2))
override def updated [B1 >: B] (key: A, value: B1): Map[A, B1] =
if (key == key1) new Map2(key1, value, key2, value2)
else if (key == key2) new Map2(key1, value1, key2, value)
else new Map3(key1, value1, key2, value2, key, value)
def + [B1 >: B](kv: (A, B1)): Map[A, B1] = updated(kv._1, kv._2)
def - (key: A): Map[A, B] =
if (key == key1) new Map1(key2, value2)
else if (key == key2) new Map1(key1, value1)
else this
override def foreach[U](f: ((A, B)) => U): Unit = {
f((key1, value1)); f((key2, value2))
}
}
class Map3[A, +B](key1: A, value1: B, key2: A, value2: B, key3: A, value3: B) extends AbstractMap[A, B] with Map[A, B] with Serializable {
override def size = 3
def get(key: A): Option[B] =
if (key == key1) Some(value1)
else if (key == key2) Some(value2)
else if (key == key3) Some(value3)
else None
def iterator = Iterator((key1, value1), (key2, value2), (key3, value3))
override def updated [B1 >: B] (key: A, value: B1): Map[A, B1] =
if (key == key1) new Map3(key1, value, key2, value2, key3, value3)
else if (key == key2) new Map3(key1, value1, key2, value, key3, value3)
else if (key == key3) new Map3(key1, value1, key2, value2, key3, value)
else new Map4(key1, value1, key2, value2, key3, value3, key, value)
def + [B1 >: B](kv: (A, B1)): Map[A, B1] = updated(kv._1, kv._2)
def - (key: A): Map[A, B] =
if (key == key1) new Map2(key2, value2, key3, value3)
else if (key == key2) new Map2(key1, value1, key3, value3)
else if (key == key3) new Map2(key1, value1, key2, value2)
else this
override def foreach[U](f: ((A, B)) => U): Unit = {
f((key1, value1)); f((key2, value2)); f((key3, value3))
}
}
class Map4[A, +B](key1: A, value1: B, key2: A, value2: B, key3: A, value3: B, key4: A, value4: B) extends AbstractMap[A, B] with Map[A, B] with Serializable {
override def size = 4
def get(key: A): Option[B] =
if (key == key1) Some(value1)
else if (key == key2) Some(value2)
else if (key == key3) Some(value3)
else if (key == key4) Some(value4)
else None
def iterator = Iterator((key1, value1), (key2, value2), (key3, value3), (key4, value4))
override def updated [B1 >: B] (key: A, value: B1): Map[A, B1] =
if (key == key1) new Map4(key1, value, key2, value2, key3, value3, key4, value4)
else if (key == key2) new Map4(key1, value1, key2, value, key3, value3, key4, value4)
else if (key == key3) new Map4(key1, value1, key2, value2, key3, value, key4, value4)
else if (key == key4) new Map4(key1, value1, key2, value2, key3, value3, key4, value)
else new HashMap + ((key1, value1), (key2, value2), (key3, value3), (key4, value4), (key, value))
def + [B1 >: B](kv: (A, B1)): Map[A, B1] = updated(kv._1, kv._2)
def - (key: A): Map[A, B] =
if (key == key1) new Map3(key2, value2, key3, value3, key4, value4)
else if (key == key2) new Map3(key1, value1, key3, value3, key4, value4)
else if (key == key3) new Map3(key1, value1, key2, value2, key4, value4)
else if (key == key4) new Map3(key1, value1, key2, value2, key3, value3)
else this
override def foreach[U](f: ((A, B)) => U): Unit = {
f((key1, value1)); f((key2, value2)); f((key3, value3)); f((key4, value4))
}
}
}
Ich denke, ich bin klarer. Für 'toMap' sollte der Builder' immaturable.Map.newBuilder' sein. Daher sollte 'empty' derjenige sein, der in' object Map' definiert ist, was 'EmptyMap.asInstanceOf [Map [A, B]]' 'ist. OTOH, '++ =' ruft das zugrundeliegende '+ =' auf, das sich auf "operator +" und "assignment" erstreckt, ersteres würde die entsprechende Methode aufrufen, die in 'object Map' definiert ist. –