trying out the prototype

[Zhong Yu]

How about this:

// any block
{
    int c;

    try FileReader reader = new FileReader( source );
    try FileWriter writer = new FileWriter( target );

    while( (c = reader.read()) != -1 )
        writer.write(c);
}

The [try ResourceSpecification] statement can appear anywhere in a
block. When the enclosing block completes, close() methods are
invoked.

It's almost as if we have destructors

public void copy(File source, File target) throws IOException
{
    int c;

    try FileReader reader = new FileReader( source );
    try FileWriter writer = new FileWriter( target );

    while( (c = reader.read()) != -1 )
        writer.write(c);

} // reader and writer will be closed upon method completion

Since we piggyback it on an existing block, we can avoid one
indentation, and making code more readable. Compatibility isn't
broken, the new behavior of the block only arise if the new type of
statement appears inside.

The "try" keyword probably sounds unnatural for this purpose. Maybe we
can use some other keyword or symbol.

IDE should warn when it appears that an auto-closeable resource is
not, but should be, initialized this way.

Note, the auto-close behavior stays the same even if the enclosing
block is a try block

try
{
    int c;

    try FileReader reader = new FileReader( source );
    try FileWriter writer = new FileWriter( target );

    while( (c = reader.read()) != -1 )
        writer.write(c);
}
catch(IOException e)
{
    // reader and writer already closed!
}

Zhong Yu



On Tue, Aug 24, 2010 at 8:40 AM, Serge Boulay <serge.boulay at gmail.com> wrote:
> The "using" block in c# only allows one resource unless the resources are of
> the same type. To use multiple resources they are nested or stacked
>
> using (StreamWriter w1 = File.CreateText("W1"))
> using (StreamWriter w2 = File.CreateText("W2"))
> {
>      // code here
> }
>
> instead of
>
> using (StreamWriter w1 = File.CreateText("W1"))
>  {
>      using (StreamWriter w2 = File.CreateText("W2"))
>      {
>          // code here
>      }
>   }
>
> Depending on the number of resources, the "using" block nesting can quickly
> get out of hand.
>
>
>
>
>
> On 8/24/10, Stephen Colebourne <scolebourne at joda.org> wrote:
>>
>> On 24 August 2010 12:14, David Holmes <David.Holmes at oracle.com> wrote:
>> >> (I guess this forms a case against the try-with-multiple-resources
>> >> statement in general. The list of semicolon-delimited declarations
>> >> enclosed by parentheses looks weird, anyway ;-)
>> >
>> > I tend to agree the syntax is awkward and far less readable than simply
>> > nesting the try-with statements.
>>
>> Overall, I think the semicolon, multi-resource, aspect is more complex
>> than the benefits it gives. Clearer code results from nesting the
>> statements.
>>
>> Stephen
>>
>>
>
>