null.scala

来自「JAVA 语言的函数式编程扩展」· SCALA 代码 · 共 82 行

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2007, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

// $Id: Null.scala 12905 2007-09-18 09:13:45Z michelou $


package scala.xml

case object Null extends MetaData {

  /** appends given MetaData items to this MetaData list */
  override def append(m: MetaData): MetaData = m

  override def containedIn1(m: MetaData): Boolean = false
  
  /** returns its argument */
  def copy(next: MetaData) = next

  override def elements = Iterator.empty

  override def filter(f: MetaData => Boolean): MetaData = this

  /** returns null */
  def getNamespace(owner: Node) = null

  final override def hasNext = false

  final override def length = 0

  final override def length(i: Int) = i

  def isPrefixed = false

  /** deep equals method */
  override def equals(that: Any) = that match {
    case m: MetaData => m.length == 0
    case _ => false
  }

  def equals1(that:MetaData) = that.length == 0

  def key = null

  def value = null

  override def map(f: MetaData => Text): List[Text] = Nil

  def next = null

  /** null */
  def apply(key: String) = {
    if(!Parsing.isNameStart (key charAt 0))
      throw new IllegalArgumentException("not a valid attribute name '"+key+"', so can never match !")
    null
  }

  /** gets value of qualified (prefixed) attribute with given key */
  def apply(namespace: String, scope: NamespaceBinding, key: String) = null

  override def hashCode(): Int = 0

  override def toString1(): String = ""

  //appends string representations of single attribute to StringBuilder
  def toString1(sb:StringBuilder) = {}

  override def toString(): String = ""

  override def toString(sb: StringBuilder): StringBuilder = sb

  override def wellformed(scope: NamespaceBinding) = true

  def remove(key: String) = this

  def remove(namespace: String, scope: NamespaceBinding, key: String) = this
}