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POWhy scala's pattern maching does not work in for loops for type matching?
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copied!<p>I'm coding against an API that gives me access to remote file system. The API returns a list of files and directories as list of node objects (parent to file and directory). </p> <p>I want to work only on a directories, ignoring files. I've tried to use type pattern matching in <code>for</code> loop but it does not work:</p> <pre><code>for { dir: CSDir <- workarea.getChildren() // <-- I'm getting an error here complaining about type conversion } { println(dir) } </code></pre> <p>Here is a similar example using scala basic objects to run it without dependencies:</p> <pre><code>val listOfBaseObjects:List[Any] = List[Any]("a string", 1:Integer); for (x: String <- listOfObjects) { println(x) } </code></pre> <p>I end up using a regular pattern matching in side of for loop and that works fine:</p> <pre><code>// This works fien for (child <- workarea.getChildren()) { child match { case dir: CSDir => println(dir) case _ => println("do not nothing") } } </code></pre> <h2>Question:</h2> <p>Can you tell me why the first /second example does not work in scala 1.9?</p> <p>In the "Programming in Scala" the <code>for</code> loop is advertised to use the same pattern matching as the <code>match</code> so it should work.</p> <p>If the for and match are different it would be great if you could point me to some articles with more details. What about pattern matching in assignment?</p> <h2>Update:</h2> <p>I can't accept an answer that states that it is impossible to skip elements in for loop as this contradicts with the "Prog. in scala". Here is a fragment from section 23.1:</p> <blockquote> <p><code>pat <- expr</code> ... The pattern <code>pat</code> gets matched one-by-one against all elements of that list. ... if the match fails, no MatchError is thrown. Instead, the element is simply discarded from the iteration</p> </blockquote> <p>and indeed the following example works just fine:</p> <pre><code>scala> val list = List( (1,2), 1, 3, (3,4)) scala> for ((x,y) <- list) { println (x +","+ y) } 1,2 3,4 </code></pre> <p>Why then type matching does not work?</p>

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