[Nice-commit] Nice/stdlib/nice/lang using.nice,NONE,1.1

[<xo...@pr...>]

Update of /cvsroot/nice/Nice/stdlib/nice/lang
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv4254/stdlib/nice/lang

Added Files:
	using.nice 
Log Message:
   Implementation of the 'using' statement, familiar from
   C#. Essentially, this code:

   let f = new FileOutputStream("hello.txt");
   using(f) 
   {
     f.write("Hello, world!".getBytes());
   }

   is equivalent to this code:

   let f = new FileOutputStream("hello.txt");
   try 
   {
     f.write("Hello, world!".getBytes());
   }
   finally
   {
     f.close();
   }

To use 'using' with your own classes, simply have them implement the abstract interface Disposable, which has only one method, void dispose();

--- NEW FILE: using.nice ---
/**************************************************************************/
/*                                N I C E                                 */
/*             A high-level object-oriented research language             */
/*                        (c) Daniel Bonniot 2003                         */
/*                                                                        */
/*  This package is free software; you can redistribute it and/or modify  */
/*  it under the terms of the GNU Lesser General Public License as        */
/*  published by the Free Software Foundation; either version 2 of the    */
/*  License, or (at your option) any later version.                       */
/*                                                                        */
/**************************************************************************/

/**
   Implementation of the <code>using</code> statement, familiar from
   C#. Essentially, this code:
   <pre>
   let f = new FileOutputStream("hello.txt");
   using(f) 
   {
     f.write("Hello, world!".getBytes());
   }
   </pre>
   is equivalent to this code:
   let f = new FileOutputStream("hello.txt");
   try 
   {
     f.write("Hello, world!".getBytes());
   }
   finally
   {
     f.close();
   }
   </pre>


   The using() method accepts any value whose type implements the 
   <code>Disposable</code> abstract interface. For instance, to make
   <code>OutputStream</code>s work with <code>using</code>, this
   code was added:
   <pre>
   class java.io.OutputStream implements Disposable;
   dispose(OutputStream s) = s.close();
   </pre>
   
   @author Bryn Keller (xo...@us...)
 */

import java.io.*;

abstract interface Disposable 
{
  void dispose();
}


<Disposable T> void using(T obj, ()->void action)
{
  try 
  {
    action();
  }
  finally
  {
    obj.dispose();
  }
}

class java.io.InputStream implements Disposable;
dispose(InputStream s) = s.close();
  
class java.io.OutputStream implements Disposable;
dispose(OutputStream s) = s.close();

class java.io.Reader implements Disposable;
dispose(Reader r) = r.close();

class java.io.Writer implements Disposable;
dispose(Writer w) = w.close();

/** For testing only */
private class NonReclosableOutputStream extends ByteArrayOutputStream {
    boolean closed = false;
    close() {
      if (closed)
	throw new IOException("Already closed");
      closed = true;
    }
  }

void _testUsing()
{
  NonReclosableOutputStream os = new NonReclosableOutputStream();
  using(os)
  {
    os.write("Hello".getBytes());
  }
  try {
    os.close();
    throw new Exception("Should have been closed!");
  } catch (IOException e) {
    //Passed.
  }
  byte[] test = "Hello".getBytes();
  byte[] output = os.toByteArray();
  assert test.length == output.length;
  for(int i = 0; i < test.length; i++) {
    assert test[i] == output[i];
  }
}