Equivalent to Java 7's Automatic Resource Management (try-with-resources)

Note that this isn't exactly new territory. People have been doing ARM
in Scala way before Java even considered it.

See http://stackoverflow.com/questions/2207425/what-automatic-resource-manag...
for some history, and
https://github.com/jsuereth/scala-arm/wiki/basic-usage for the most
advanced library available (afaik).

On Fri, Aug 26, 2011 at 19:18, Todd Vierling wrote:
> In my personal Scala code playground, I've been tinkering with something
> that would auto-close resources at the end of a block for a while, and I've
> cleaned up my implementation to be self-encapsulated:
> https://github.com/tvierling/duh-util/blob/master/src/main/scala/org/duh...
>
> This introduces an implicit wrapper (AutoClose.RichCloseable) that provides
> two forms of an added method "autoClose": one uses a by-name block; the
> other will provide the wrappered resource as a single argument. This wrapper
> works automatically with any class exposing a zero-arg close() method, which
> means that it works under all supported Java versions, not just 7+.
> This implements the same overall semantics as Java 7's try-with-resources
> construct. It only handles one resource per nesting level, unlike the more
> complicated Java 7 syntax, but usage is pretty straightforward. Here's an
> example of both syntax forms; you'll note that the "out =>" version is the
> closest simulation of the Java 7 feature, as the value is not accessible
> outside the block:
> def doStuff(in: InputStream) {
>   in.autoClose {
>     new FileOutputStream("foo").autoClose { out =>
>       out.write(/* ... */)
>     }
>     // out is now closed
>   }
>   // in is now closed
> }
> There's added logic in this implementation to provide built-in support for
> the Java 7+ suppressed-Throwable feature if the code is running under Java 7
> or later, and a fallback mechanism for earlier versions (a pluggable
> InheritableThreadLocal of a handler function, which may perform special
> duties with to-be-suppressed Throwables under Java 6 or earlier).
> As a speed hack, it uses a match expression on the wrapped object when
> finally calling close(), matching against several commonly used JDK classes
> with close() methods before deferring to the slower structural type logic.
> The truly important part of that match expression (IMO) is the match against
> java.io.Closeable; the others are a bit less important.
> Other code in my playground reserves copyright just to keep from tripping up
> people with my probably-broken code (see README.md at top of the Github
> project), but I have released this specific source file to the public
> domain. If EPFL would like to include a version of this implementation in
> the standard Scala library, please feel free. Attribution in the derived
> source file would be nice, but is not required.
> Thoughts and suggestions are always welcome.
>

Note that this isn't exactly new territory. People have been doing ARM
in Scala way before Java even considered it.

On Friday, August 26, 2011 6:38:40 PM UTC-4, Daniel Sobral wrote:

Note that this isn't exactly new territory. People have been doing ARM
in Scala way before Java even considered it.

Odd. When I originally went looking, I couldn't find such an implementation for some reason — but then, I'd been sitting on this for well over a year and letting it rot. Thanks for the pointers!

On Fri, Aug 26, 2011 at 8:48 PM, Josh Suereth wrote:
> If you have a look at the ARM library, let me know what you think.  I'm
> trying to go 1.0 shortly, so any suggestions before the release are welcome!

I'm taking a look at it this week. Cursory glance, it looks like some
hooking into the Java 7 suppressed exceptions mechanism could be added
(it can be made runtime-conditional with very low overhead, which I
did for my tiny implementation).

However, I don't yet know how your library handles multiple exceptions
thrown by cleanup routines, so I'll have to grok that first.

On Fri, Aug 26, 2011 at 8:48 PM, Josh Suereth <joshua.suereth@gmail.com> wrote:
> If you have a look at the ARM library, let me know what you think.  I'm
> trying to go 1.0 shortly, so any suggestions before the release are welcome!

I'm taking a look at it this week. Cursory glance, it looks like some
hooking into the Java 7 suppressed exceptions mechanism could be added
(it can be made runtime-conditional with very low overhead, which I
did for my tiny implementation).

However, I don't yet know how your library handles multiple exceptions
thrown by cleanup routines, so I'll have to grok that first.

--

On Mon, Aug 29, 2011 at 8:56 PM, Josh Suereth wrote:
> I can add the low-overhead exception supressing mechanism.  If you want to
> contribute anything to the project, feel free to do so!

Github-forked and will get back to you soon.