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POReplacement for specialization of method parameters in subclasses
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  1. POReplacement for specialization of method parameters in subclasses
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    copied!<p>I would like to create a framework where users are able to subclass a base class, <code>Node</code> which is able to produce a message (here an integer) based on the current instance state, and the properties of another instance (the parameter n). The users should be able to specialize the method <code>getMessage</code> to produce different messages based on the class of the current instance and <em>the class of the parameter n</em>, as shown in the code below.</p> <p>The function <code>importantAlgorithm</code> uses messages generated by these nodes to compute the final results.</p> <pre><code>// Classes defined by the framework // abstract class Node { def getMessage(n: Node) : Int } def importantAlgorithm(lstNodes1: List[_ &lt;: Node], lstNodes2: List[_ &lt;: Node]) = { val results = lstNodes1.zip(lstNodes2).map({case (n1, n2) =&gt; // I would like to get the proper message *BASED ON // THE TYPE OF N1 and N2* val message = n1.getMessage(n2) // Do some work with the message //... //... }) //... } // Classes defined by framework users // class ItemNode(val p: Int) extends Node { override def getMessage(n: UserNode) = { // Compute message based on this ItemNode member variables // and n (instance of UserNode) member variables } override def getMessage(n: ItemNode) = { // Compute message based on this ItemNode member variables // and n (instance of UserNode) member variables // The algorithm is different from the algorithm // used in the previous method } } class UserNode extends Node { override def getMessage(n: OtherNode) = { // Compute message. Same idea as above } } class OtherNode extends Node { override def getMessage(n: UserNode) = { // Compute message. Same idea as above } } // The user should be able to use the framework this way importantAlgorithm(List(new UserNode(), new ItemNode(236), new OtherNode(), List(new OtherNode(), new ItemNode(542), new UserNode())) </code></pre> <p>Of course, Scala does not allow to specialize a parameter of a method in a subclass and the above code does not compile. I could use <code>isInstanceOf[]</code> or RTTI but I have a feeling that I am not thinking properly and not designing my framework properly. <strong>How could I replace the mechanism described in the code sample above by a simpler and cleaner solution ?</strong></p>
 

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