On Mon, 21 Feb 2011, Nick wrote:
> On 21/02/11 07:20, Junio C Hamano wrote:
> > If we are going to change things so that everybody uses a
> > more traditional "eval {}; if ($@) { ... }", it would be a welcome change
> > from my point of view.
>
> A small aside - note the "Dangers of using $@" described here:
>
> http://www.socialtext.net/perl5/exception_handling
>
> To paraphrase, this:
>
> eval { stuff ; 1} or do { handle_exception };
>
> is marginally safer than:
>
> eval { stuff }; if (defined $@) { handle_exception }
Important note: it is "if ($@)", not "if (defined $@)":
If there was no error, $@ is guaranteed to be a null string.
^^^^^^^^^^^
It is empty string, not undef.
> because it is possible that $@ can be modified (say, by a DESTROY method) before
> the if clause sees it. The former idiom does not stop that, it just means your
> exception handler is executed reliably.
>
> Normally it is not a problem, but this is still something worth knowing.
Or better use Try::Tiny, which takes care of this and more
use Try::Tiny;
try { stuff } catch { handle_exception };
--
Jakub Narebski
Poland
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