Question

在Scala 2.10中不推荐使用Elem（prefix，label，attribs，scope，child）方法，应使用Elem（前缀，标签，attribs，scope，minimizeEmpty，child）。但是至少在空元素上，新的apply方法具有不同的行为。不推荐的版本以这种方式工作：

val inputXML = <PC Price="100" CurrencyCode="USD"/>
val rule1 = new RewriteRule {
    override def transform(n: Node): Seq[Node] = n match {
        case Elem(prefix, "PC", attribs, scope, content @ _*)  => 
            Elem(prefix, "Mac", attribs, scope, content:_*)
        case other => other
    }
}

println(new RuleTransformer(rule1).transform(inputXML))

打印：

List(<Mac Price="100" CurrencyCode="USD"/>)

但是当使用新的Elem方法时，匹配不起作用：

val inputXML = <PC Price="100" CurrencyCode="USD"/>
val rule1 = new RewriteRule {
    override def transform(n: Node): Seq[Node] = n match {
        case Elem(prefix, "PC", attribs, scope, minimizeEmpty, content @ _*)  => 
            Elem(prefix, "Mac", attribs, scope, true, content:_*)
        case other => other
    }       
}

println(new RuleTransformer(rule1).transform(inputXML))

上面的代码返回：

<PC Price="100" CurrencyCode="USD"/>

这是一个错误还是我做错了什么？我正在使用Scala 2.10.2。

谢谢，

Answer 1

unapply中只有一个Elem方法：

def unapplySeq(n: Node): Option[(String, String, scala.xml.MetaData, scala.xml.NamespaceBinding, Seq[scala.xml.Node])]

它返回Tuple5，但您尝试使用它，就像返回Tuple6一样。您无法使用minimizeEmpty方法获取unapplySeq。

val inputXML = <PC Price="100" CurrencyCode="USD"/>
val rule1 = new RewriteRule {
    override def transform(n: Node): Seq[Node] = n match {
        case Elem(prefix, "PC", attribs, scope, content @ _*)  => 
            Elem(prefix, "Mac", attribs, scope, true, content:_*)
        case other => other
    }       
}

println(new RuleTransformer(rule1).transform(inputXML))
// List(<Mac Price="100" CurrencyCode="USD"/>)

但我想这里有一个错误。此方法应命名为unapply以显示编译错误：

object ElemHelper {
  def unapply(n: Node): Option[(String, String, scala.xml.MetaData, scala.xml.NamespaceBinding, Seq[scala.xml.Node])] = Elem.unapplySeq(n)
}

val rule1 = new RewriteRule {
    override def transform(n: Node): Seq[Node] = n match {
        case ElemHelper(prefix, "PC", attribs, scope, minimizeEmpty, content @ _*)  => 
            Elem(prefix, "Mac", attribs, scope, true, content:_*)
        case other => other
    }       
}

// <console>:16: error: wrong number of arguments for object ElemHelper

我创建了bug report。

Scala中的XML - 使用minimizeEmpty布尔值的Elem方法

1 个答案: