I think my head just exploded in a cloud of purple smoke.
On Tue, May 30, 2017 at 10:03 AM, <p...@cpan.org> wrote:
> Hi!
>
> Please note that true value in $@ is *not* necessary condition for
> checking if error in eval occurred. And similarly empty string or logic
> false value in $@ is *not* necessary condition that eval succeeded.
>
> The only thing which is guaranteed is undef return value from eval in
> case it failed. So correct check is:
>
> my $success = eval {
> # MY CODE
> 1;
> };
>
> unless ($success) {
> # HANDLE ERROR, $@ may (but does not have to) contain error
> }
>
> "1;" in eval block is there to set $success to 1. In case MY CODE throw
> error, $success is set to undef by perl.
>
> Note that $@ is propagated back, so you should localize $@ before
> calling eval. This is especially required if MY CODE (or function called
> from MY CODE) calls also eval.
>
> So you can use this pattern:
>
> {
> local $@;
> eval {
> # MY CODE
> 1;
> } or do {
> # HANDLE ERROR in $@ (but may be undef!)
> };
> }
>
> If you do not write 1; then return value is taken from the last call in
> MY CODE. So if problem is also when last function return non zero, then
> you can remove "1;". You can also combine it with "and" block, but
> beware for and/or logical blocks:
>
> {
> local $@;
> eval {
> func_which_may_die_or_fail_with_zero();
> } and do {
> print "function succeeded\n";
> func_may_fail_with_zero();
> } or do {
> my $err = $@ || 'unknown error';
> warn "Error: $err\n";
> rollback();
> };
> }
>
> But I suggest to use module like Try::Tiny or Try::Catch which handle
> above eval and $@ logic for you and you can easily write:
>
> try {
> # MY CODE
> } catch {
> # HANDLE ERROR in $_ (may be undef!)
> my $err = $_ || 'unknown error';
> };
>
> On Tuesday 30 May 2017 09:39:53 John Dunlap wrote:
> > Yes, I do that extensively and it works perfectly. It's as close to a
> true
> > Try/Catch block as we have in the perl world. However, I *usually* do not
> > return values from it because I use this construct to control my database
> > transaction demarcation and using the return value from outside of the
> eval
> > wouldn't be inside the transaction. With that said, I have had to do it
> > from time to time and it works just fine. Also, it is advisable to copy
> the
> > contents of $@ into a separate variable immediately. My understanding is
> > that this can prevent some weird concurrency issues, under some
> conditions.
> > My general form looks something like this,
> >
> > my $return = eval {
> > # BEGIN DATABASE TRANSACTION
> >
> > # DO SOME STUFF
> >
> > # COMMIT DATA BASE TRANSACTION
> >
> > return 'SOME VALUE';
> > };
> >
> > if ($@) {
> > my $error = $@;
> >
> > # ROLLBACK DATABASE TRANSACTION
> >
> > # LOG ERROR
> > }
> >
> >
> > On Tue, May 30, 2017 at 4:47 AM, James Smith <j...@sanger.ac.uk> wrote:
> >
> > > Not really a mod_perl question but you can always wrap your method
> call in
> > > an eval
> > >
> > > my $ret = eval { $m->...() };
> > >
> > > And then check $@ for the error message
> > >
> > >
> > > On 2017-05-26 02:08 AM, Peng Yonghua wrote:
> > >
> > >> greeting,
> > >>
> > >> I am not so good at perl/modperl,:)
> > >>
> > >> In the handler, a method from a class was called, when something dies
> > >> from within the method, what's the correct way the handler will take?
> > >>
> > >> for example, I wrote this API which works right if given a correct
> domain
> > >> name:
> > >>
> > >> http://fenghe.org/domain/?d=yahoo.com
> > >>
> > >> server response:
> > >> var data={"registration":"domain may be taken","domain":"yahoo.com"}
> > >>
> > >> If given a wrong domain name:
> > >>
> > >> http://fenghe.org/domain/?d=yahoo.nonexist
> > >>
> > >> The server returns 500.
> > >>
> > >> This is because, in the handler, I used this module (wrote also by
> me):
> > >>
> > >> http://search.cpan.org/~pyh/Net-Domain-Registration-Check-0.
> > >> 03/lib/Net/Domain/Registration/Check.pm
> > >>
> > >> And in the module, croak like this was happened,
> > >>
> > >> croak "domain TLD not exists" unless tld_exists($tld);
> > >>
> > >> When handler meets the croak, it dies (I guess) and server returns
> 500.
> > >>
> > >> How will I make the full system work right? fix on handler, or the
> module
> > >> itself?
> > >>
> > >> Thanks.
> > >>
> > >
> > >
> > >
> > > --
> > > The Wellcome Trust Sanger Institute is operated by Genome Research
> > > Limited, a charity registered in England with number 1021457 and a
> company
> > > registered in England with number 2742969, whose registered office is
> 215
> > > Euston Road, London, NW1 2BE.
> >
> >
> >
> >
> > --
> > John Dunlap
> > *CTO | Lariat *
> >
> > *Direct:*
> > *j...@lariat.co <j...@lariat.co>*
> >
> > *Customer Service:*
> > 877.268.6667
> > supp...@lariat.co
>
--
John Dunlap
*CTO | Lariat *
*Direct:*
*j...@lariat.co <j...@lariat.co>*
*Customer Service:*
877.268.6667
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