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copied!<p>Here's <a href="https://stackoverflow.com/users/65133/james-iry">James Iry</a> solution using continuations:</p> <pre><code>// standard using block definition def using[X <: {def close()}, A](resource : X)(f : X => A) = { try { f(resource) } finally { resource.close() } } // A DC version of 'using' def resource[X <: {def close()}, B](res : X) = shift(using[X, B](res)) // some sugar for reset def withResources[A, C](x : => A @cps[A, C]) = reset{x} </code></pre> <p>Here are the solutions with and without continuations for comparison:</p> <pre><code>def copyFileCPS = using(new BufferedReader(new FileReader("test.txt"))) { reader => { using(new BufferedWriter(new FileWriter("test_copy.txt"))) { writer => { var line = reader.readLine var count = 0 while (line != null) { count += 1 writer.write(line) writer.newLine line = reader.readLine } count } } } } def copyFileDC = withResources { val reader = resource[BufferedReader,Int](new BufferedReader(new FileReader("test.txt"))) val writer = resource[BufferedWriter,Int](new BufferedWriter(new FileWriter("test_copy.txt"))) var line = reader.readLine var count = 0 while(line != null) { count += 1 writer write line writer.newLine line = reader.readLine } count } </code></pre> <p>And here's Tiark Rompf's suggestion of improvement:</p> <pre><code>trait ContextType[B] def forceContextType[B]: ContextType[B] = null // A DC version of 'using' def resource[X <: {def close()}, B: ContextType](res : X): X @cps[B,B] = shift(using[X, B](res)) // some sugar for reset def withResources[A](x : => A @cps[A, A]) = reset{x} // and now use our new lib def copyFileDC = withResources { implicit val _ = forceContextType[Int] val reader = resource(new BufferedReader(new FileReader("test.txt"))) val writer = resource(new BufferedWriter(new FileWriter("test_copy.txt"))) var line = reader.readLine var count = 0 while(line != null) { count += 1 writer write line writer.newLine line = reader.readLine } count } </code></pre>

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