I had an interesting glitch occur to me today. I had some code like

eval {
  for my $case ( @cases ) {
    if (!interesting($case)) {
       next;
    } 
    process($case);
  }
};
[download]

The problem was that both interesting() and process() would die for certain error cases. And instead of skipping all the cases on first error i wanted to see all the errors, so I changed to code to something like this:

  for my $case ( @cases ) {
    eval {
      if (!interesting($case)) {
         next;
      } 
      process($case);
    };
    if ($@) {
      print "$case had errors:$@";
    }
  }
[download]

I was a little surprised to discover that now all of my cases were failing. What took me a while to work out was that I had

use warnings FATAL=>'all';
[download]

in the code. Nexting out of an eval is a warning, and by promoting the warnings to a fatal the resulting behaviour of the code was fundamenetally changed.

So next time you decide to use warnings fatal do yourself a favour and do a code review of any evals that you are using. Heres an example of the issue.

#!perl -l
$|++;
use strict;
use warnings;
use warnings FATAL => 'all';
no warnings 'exiting'; # comment this out to change behaviour.

{ eval { next }; print "foo" } print "bar";
print "---";
for (1..10) { 
  eval {  
         print "bar";  
         next; 
         print "foo"; 
  };  
  print "Baz"; 
}
[download]

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