Question

I have an API (from third party java library) that looks like:

public List<?> getByXPath(String xpathExpr)

defined on a class called DomNode

I try this in scala:

node.getByXPath(xpath).toList.foreach {node: DomElement => 

   node.insertBefore(otherNode)   

}

But I get compile error on node.getByXPath.
error: “type mismatch; found : (com.html.DomElement) => Unit required: (?0) => ? where type ?0”

If I change it into:

node.getByXPath(xpath).toList.foreach {node => 

   node.insertBefore(otherNode)   

}

then the error goes away but then I get error on node.insertBefore(otherNode)
error: “value insertBefore is not a member of ?0”

What is the answer to this problem?

Answer 1

You’ll have to cast it. ie,

node.getByXPath(xpath).toList.foreach {node => 
   node.asInstanceOf[DomElement].insertBefore(otherNode)   
}

You would have the same issue in Java as the type of List elements is unknown.

(I am assuming every element actually is a DomElement)

EDIT:

Daniel is right, there is a better way to do this. For example, you can throw a much nicer exception (as compared to ClassCastException or MatchError). Eg.

node.getByXPath(xpath).toList.foreach { 
    case node: DomElement => node.insertBefore(otherNode)  
    case _: => throw new Exception("Expecting a DomElement, got a " + node.getClass.getName)   
}