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Re: telling the javac that a method doesn't return at all...

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On Friday, February 28, 2014 9:10:57 AM UTC-8, Andreas Leitgeb wrote:
> May be a wish to the easter bunny, or I might just have missed it
> 
> so far (like some easter egg)
> 
> 
> 
> Suppose I have some "doCleanUpAndExit" method, that in the
> 
> end either calls System.exit() or throws some Error or custom 
> 
> RuntimeException.
> 
> 
> 
> I'd like the compiler to *know* that this method cannot possibly
> 
> return, and that any code following it should be considered 
> 
> as "unreachable" code by the compiler.
> 
> 
> 
> E.g., I'd have code like:
> 
> 
> 
> class Foo {
> 
>    @DoesntReturn // tell compiler this method isn't supposed to return
> 
>    public void doCleanUpAndExit() {
> 
>       // compiler would barf if there was any "return"
> 
>       //  or possible flow to end of method.
> 
>       throw new ThisIsTheEndException();
> 
>       // or System.exit(); which would itself need to be thusly flagged.
> 
>    }
> 
>    // test1() and test2() are boolean-returning methods...
> 
>    public boolean check() {
> 
>       if ( ! test1() ) { // aww, it's all borked up
> 
>          doCleanUpAndExit();
> 
>          // any further code here would make the compiler barf
> 
>       } else {
> 
>          return ( test2() );
> 
>       }
> 
>       // compiler should know that flow won't ever arrive here,
> 
>       //   so there is no way that the method doesn't return a boolean..
> 
>    }
> 
> }
> 
> 
> 
> Did I miss some annotation that already does this?
> 
> Is there anything like this already in the queue for 
> 
>   future Java versions?
> 
> 
> 
> Thanks in advance.
> 
> 
> 
> PS: I've already defined a "WontEverGetHereException" to throw
> 
>   at certain places, where the compiler otherwise barfed about
> 
>   possible non-returning exits from value returning methods, so
> 
>   I'm rather asking out of curiosity for nicer solutions than
> 
>   facing a real problem. Still I'd rather have it a compile-time
> 
>   barf than a run-time barf if my assumptions were wrong w.r.t
> 
>   possible flow...
> 
> 
> 
> PPS: any enlightenment about why this could be wrong-headed would
> 
>   also be appreciated, except if it boils down to pointing out the
> 
>   intended "exceptional" semantics of exceptions...  Calling those
> 
>   non-returning methods itself would only happen exceptionally.

1. Define doCleanUpAndExit() to return, say, a bool.
2. Define a constructor WontEverGetHereException(bool).  (WontEverGetHereException needs to be a RuntimeException.)
3. Exit via 

    throw new WontEverGetHereException(doCleanUpAndExit())

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Thread

telling the javac that a method doesn't return at all... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-02-28 17:10 +0000
  Re: telling the javac that a method doesn't return at all... Lew <lewbloch@gmail.com> - 2014-02-28 16:13 -0800
    Re: telling the javac that a method doesn't return at all... Jeff Higgins <jeff@invalid.invalid> - 2014-03-01 09:12 -0500
      Re: telling the javac that a method doesn't return at all... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-03-05 13:06 +0000
  Re: telling the javac that a method doesn't return at all... Roedy Green <see_website@mindprod.com.invalid> - 2014-03-01 01:10 -0800
    Re: telling the javac that a method doesn't return at all... Jeff Higgins <jeff@invalid.invalid> - 2014-03-01 08:44 -0500
  Re: telling the javac that a method doesn't return at all... Arne Vajhøj <arne@vajhoej.dk> - 2014-03-01 22:02 -0500
    Re: telling the javac that a method doesn't return at all... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-03-05 13:31 +0000
      Re: telling the javac that a method doesn't return at all... Arne Vajhøj <arne@vajhoej.dk> - 2014-03-11 20:11 -0400
        Re: telling the javac that a method doesn't return at all... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-03-12 10:17 +0000
  Re: telling the javac that a method doesn't return at all... Mike Amling <mamling@chaff.us> - 2014-03-04 13:19 -0600
    Re: telling the javac that a method doesn't return at all... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-03-05 13:39 +0000
  Re: telling the javac that a method doesn't return at all... mike.s.schilling@gmail.com - 2014-03-04 19:30 -0800
    Re: telling the javac that a method doesn't return at all... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-03-09 14:33 +0000
  Re: telling the javac that a method doesn't return at all... Silvio <silvio@internet.com> - 2014-03-12 14:03 +0100
  Re: telling the javac that a method doesn't return at all... Michal Kleczek <michal_wytnijto@kleczek.org> - 2014-03-19 11:51 +0100
    Re: telling the javac that a method doesn't return at all... Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> - 2014-03-19 12:28 +0000
      Re: telling the javac that a method doesn't return at all... Michal Kleczek <michal_wytnijto@kleczek.org> - 2014-03-23 11:15 +0100

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