On 3/7/06, Chas Owens <[EMAIL PROTECTED]> wrote:
> On 3/7/06, Jay Savage <[EMAIL PROTECTED]> wrote:
> snip
> > Since eval traps die, 'eval{ eval {} or die [EMAIL PROTECTED];};' is a
> > convenient
> > method for propagating $@ out of deeply nested evals. It's just a way
> > to save writing lots of if blocks that do nothing but pass $@ along.
> snip
>
> You had better be careful with the 'or' there. The return value of an
> eval is that of the last statement executed. This means that
>
> eval { $a = 0 } or die $@ ;
>
> will fail even though the block did not have an error. The safe way
> to handle blocks is to check the value of $@ and die if it is set:
>
> eval { $a = 0 };
> die $@ if defined $@;
>
> Although I believe you can always get away with shortening it to
>
> eval { $a = 0 };
> die $@ if $@;
>
> since die() always (I think) adds on "at X line Y.".
>
That's a good point to keep in mind, but here OP clearly wants to
return 1 for success. I said it was a shortcut; YMMV on corner cases.
Another neat (sometimes) trick with eval is just to use a bare die as
in 'die if $@'. That will append '\t...propagated at line $x\n' to the
end of $@ every time the error is proagated by a nested eval. It can
help you trace the execution and is either very useful or supremely
annoying, depending on the situation.
-- jay
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