Re: [Templates] Template Toolkit and DateTime::Duration

>Arshavir Grigorian wrote:

Thanks for the test script. I'll be sure to write one up next time.

To see the problem, the DateTime::Duration object needs to be more than 
1 level deep, like so:

  use strict;
  use warnings;
  use Template;
  use DateTime::Duration;

  my $template = Template->new();
  my $duration = DateTime::Duration->new( years => 3 );
  my %top =  ( duration => $duration );

  $template->process(\*DATA, { top => \%top })
      || die $template->error();

  __DATA__
  [% IF top.duration.years -%]
  *  The duration is: [% top.duration.years %] years
  [% ELSE -%]
  *  The duration is less than a year.
  [% END -%]

My fix has worked fine for me. DateTime's author, Dave Rolsky suggested 
an even better fix:

use Scalar::Util qw(refaddr);
my $atroot = ref $root && refaddr($root) == refaddr($self);

There is probably a good reason why the compare method is not 
overloaded. Dave is probably the best person to answer that.

I agree that adding any code to a subroutine that gets executed for 
every dot operation can be problematic. On the other hand, checking 
whether 2 references point to the same memory location is the most sure 
way to know whether 2 objects are the same.

Arshavir

Andy Wardley wrote:

>Arshavir Grigorian wrote:
>  
>
>>I am trying to access a DateTime::Duration method from within my TT 
>>template and getting an getting the following exception:
>>    
>>
>
>I don't see any problem.  Here's my test script:
>
>  use strict;
>  use warnings;
>  use Template;
>  use DateTime::Duration;
>
>  my $template = Template->new();
>  my $duration = DateTime::Duration->new( years => 3 );
>
>  $template->process(\*DATA, { duration => $duration })
>      || die $template->error();
>
>  __DATA__
>  [% IF duration.years -%]
>  *  The duration is: [% duration.years %] years
>  [% ELSE -%]
>  *  The duration is less than a year.
>  [% END -%]
>
>I get the correct output and no exception.  Can you "fix" my example to 
>demonstrate the problem?
>
>  
>
>>If we replace it with the following, the logic 
>>will short circuit and we will never have to compare apples to oranges.
>>
>>my $atroot = ((ref ($root) eq ref ($self)) && ($root eq $self));
>>
>>It should not break anything else. Right?
>>    
>>
>
>Who knows?  That's what the test suite is for.  :-)
>
>If you have something that looks like a bug, you need to write a short test 
>like the above that clearly demonstrates the problem, add it to the test 
>suite, apply the fix, and then run the test suite to prove that the fix 
>fixes the bug and doesn't break anything else.
>
>But I'm not in favour of adding a hack in TT to work around one particular
>module's problems, especially when it's adding extra code that will be 
>executed every time every node of every dotted variable is evaluated in 
>every template in every TT installation across the World.  That's an awful 
>lot of dotops.  :-)
>
>It would be much easier to fix the real problem in DateTime::Duration
>which overloads <=> and cmp to _compare_overload() but then dies when
>it actually gets called:
>
>  sub _compare_overload
>  {
>      die "DateTime::Duration does not overload comparison.  See the documentation on the compare() method for details.";
>  }
>
>
>A
>
>  
>

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