request switch statement with common block

[H. S. Teoh]

On Sat, Aug 03, 2013 at 02:34:51PM -0700, Jonathan M Davis wrote:
> On Saturday, August 03, 2013 14:25:24 H. S. Teoh wrote:
> > On Sat, Aug 03, 2013 at 01:33:44PM -0700, Jonathan M Davis wrote:
[...]
> > > I definitely use scope from time to time, but I don't know how
> > > frequently I use it in comparison to how often I should use it. I
> > > was actually using scope(success) more until someone pointed out
> > > that there's an efficiency hit with that as it was putting
> > > try-catch blocks in places where there wouldn't have been before
> > > (as opposed to scope(exit) or scope(failure) where you'd be using
> > > try-catch blocks if you weren't using scope).
> > 
> > [...]
> > 
> > Hmm, I never thought of that. So that limits the use cases of scope
> > guards even more. :-P
> 
> Yeah. For instance, I'd made it so that RedBlackTree was using
> scope(success) for mutating its length in a few places, which helped
> make the code cleaner (because you didn't have to worry about
> incrementing the length at each of the various return statements), but
> that introduced try-catch blocks where there otherwise wouldn't have
> been any, and that code definitely needs to be as efficient as
> possible, so the scope(success) statements were removed from there.
> Other code wouldn't care as much, but for something like RedBlackTree,
> it really matters. It is a bit of a shame though, since it made the
> code cleaner.
[...]

On second thoughts, why is scope(success) implemented as try/catch?
Shouldn't the compiler be able to insert it before the end of each block
instead? Stack-unwinding bypasses the end of block code, so the only way
you can get there is by successful exit.


T

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