Perl::CPreirtli:c::C:rPiotliicc:y::P:oEUlrsirecoryr:HC:aoEnnrdtrlroiirnbHgua:tn:edRdleiqPnuegir:rl:eRCDehoqecucuikmrieennCgthRaeetctikuoirnnngVRaeltuuerOnfVEavlaule(O3f)Eval(3)



NNAAMMEE
       Perl::Critic::Policy::ErrorHandling::RequireCheckingReturnValueOfEval -
       You can't depend upon the value of "$@"/"$EVAL_ERROR" to tell whether
       an "eval" failed.

AAFFFFIILLIIAATTIIOONN
       This Policy is part of the core Perl::Critic distribution.

DDEESSCCRRIIPPTTIIOONN
       A common idiom in perl for dealing with possible errors is to use
       "eval" followed by a check of $@/$EVAL_ERROR:

           eval {
               ...
           };
           if ($EVAL_ERROR) {
               ...
           }

       There's a problem with this: the value of $EVAL_ERROR can change
       between the end of the "eval" and the "if" statement.  The issue is
       object destructors:

           package Foo;

           ...

           sub DESTROY {
               ...
               eval { ... };
               ...
           }

           package main;

           eval {
               my $foo = Foo->new();
               ...
           };
           if ($EVAL_ERROR) {
               ...
           }

       Assuming there are no other references to $foo created, when the "eval"
       block in "main" is exited, "Foo::DESTROY()" will be invoked, regardless
       of whether the "eval" finished normally or not.  If the "eval" in
       "main" fails, but the "eval" in "Foo::DESTROY()" succeeds, then
       $EVAL_ERROR will be empty by the time that the "if" is executed.
       Additional issues arise if you depend upon the exact contents of
       $EVAL_ERROR and both "eval"s fail, because the messages from both will
       be concatenated.

       Even if there isn't an "eval" directly in the "DESTROY()" method code,
       it may invoke code that does use "eval" or otherwise affects
       $EVAL_ERROR.

       The solution is to ensure that, upon normal exit, an "eval" returns a
       true value and to test that value:

           # Constructors are no problem.
           my $object = eval { Class->new() };

           # To cover the possiblity that an operation may correctly return a
           # false value, end the block with "1":
           if ( eval { something(); 1 } ) {
               ...
           }

           eval {
               ...
               1;
           }
               or do {
                   # Error handling here
               };

       Unfortunately, you can't use the "defined" function to test the result;
       "eval" returns an empty string on failure.

       "But we don't use _D_E_S_T_R_O_Y_(_) anywhere in our code!" you say.  That may
       be the case, but do any of the third-party modules you use have them?
       What about any you may use in the future or updated versions of the
       ones you already use?

CCOONNFFIIGGUURRAATTIIOONN
       This Policy is not configurable except for the standard options.

SSEEEE AALLSSOO
       See thread on perl5-porters starting here:
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-06/msg00537.html
       <http://www.xray.mpe.mpg.de/mailing-
       lists/perl5-porters/2008-06/msg00537.html>.

AAUUTTHHOORR
       Elliot Shank "<perl@galumph.com>"

CCOOPPYYRRIIGGHHTT
       Copyright (c) 2008-2010 Elliot Shank.

       This program is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.  The full text of this license can
       be found in the LICENSE file included with this module.



perl v5P.e1r2l.:2:Critic::Policy::ErrorH2a0n1d3l-i0n2g-:2:6RequireCheckingReturnValueOfEval(3)
