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    <p>Chris Hansen's <a href="http://polyglot-window.blogspot.com/2009/03/arm-blocks-in-scala-revisited.html" rel="noreferrer">blog entry 'ARM Blocks in Scala: Revisited' from 3/26/09</a> talks about about slide 21 of Martin Odersky's <a href="http://www.scala-lang.org/node/1261" rel="noreferrer">FOSDEM presentation</a>. This next block is taken straight from slide 21 (with permission): </p> <pre><code>def using[T &lt;: { def close() }] (resource: T) (block: T =&gt; Unit) { try { block(resource) } finally { if (resource != null) resource.close() } } </code></pre> <p>--end quote--</p> <p>Then we can call like this:</p> <pre><code>using(new BufferedReader(new FileReader("file"))) { r =&gt; var count = 0 while (r.readLine != null) count += 1 println(count) } </code></pre> <p>What are the drawbacks of this approach? That pattern would seem to address 95% of where I would need automatic resource management...</p> <p><strong>Edit:</strong> added code snippet</p> <hr> <p><strong>Edit2:</strong> extending the design pattern - taking inspiration from python <code>with</code> statement and addressing:</p> <ul> <li>statements to run before the block </li> <li>re-throwing exception depending on the managed resource</li> <li>handling two resources with one single using statement</li> <li>resource-specific handling by providing an implicit conversion and a <code>Managed</code> class</li> </ul> <p>This is with Scala 2.8.</p> <pre><code>trait Managed[T] { def onEnter(): T def onExit(t:Throwable = null): Unit def attempt(block: =&gt; Unit): Unit = { try { block } finally {} } } def using[T &lt;: Any](managed: Managed[T])(block: T =&gt; Unit) { val resource = managed.onEnter() var exception = false try { block(resource) } catch { case t:Throwable =&gt; exception = true; managed.onExit(t) } finally { if (!exception) managed.onExit() } } def using[T &lt;: Any, U &lt;: Any] (managed1: Managed[T], managed2: Managed[U]) (block: T =&gt; U =&gt; Unit) { using[T](managed1) { r =&gt; using[U](managed2) { s =&gt; block(r)(s) } } } class ManagedOS(out:OutputStream) extends Managed[OutputStream] { def onEnter(): OutputStream = out def onExit(t:Throwable = null): Unit = { attempt(out.close()) if (t != null) throw t } } class ManagedIS(in:InputStream) extends Managed[InputStream] { def onEnter(): InputStream = in def onExit(t:Throwable = null): Unit = { attempt(in.close()) if (t != null) throw t } } implicit def os2managed(out:OutputStream): Managed[OutputStream] = { return new ManagedOS(out) } implicit def is2managed(in:InputStream): Managed[InputStream] = { return new ManagedIS(in) } def main(args:Array[String]): Unit = { using(new FileInputStream("foo.txt"), new FileOutputStream("bar.txt")) { in =&gt; out =&gt; Iterator continually { in.read() } takeWhile( _ != -1) foreach { out.write(_) } } } </code></pre>
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    1. POWhat Automatic Resource Management alternatives exist for Scala?
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    1. COThere are alternatives, but I don't meant to imply there's something wrong with that. I just want all those answers here, on Stack Overflow. :-)
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      1. USDaniel C. Sobral
 

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