I've put together a test script demonstrating how my data model works. Please tell me this fails for you, or I might go insane. Bonus points if you can tell me how to fix it.

#!/usr/bin/perl

use strict;
use warnings;
use Template;

my $container = Container->new();
$container->add( 
  Object->new( name => 'foo', value => 10, usefulness => 0 )
);
$container->add(
  Object->new( name => 'bar', value => 20, meaning => 42 )
);

my $vars = {
  'container' => $container
};

my $template = <<EOT;
container=[% container %]
all:
[% FOREACH element IN container.all.sort('name') %]
[% element %] name is [% element.name %]
[% END %]
one:
[% FOREACH element IN container.one(10).sort('name') %]
[% element %] name is [% element.name %]
[% END %]
EOT

my $tt = Template->new();
$tt->process(\$template, $vars);

package Object;

sub new {
  my $class = shift;
  my $self = {@_};
  return bless($self, $class); 
}


package Container;

sub new {
  my $class = shift;
  my $self = {@_};
  return bless($self, $class); 
}

sub add {
  my $self = shift;
  my $new = shift;
  push @{$self->{'objects'}}, $new;
}

sub all {
  my $self = shift;
  return @{$self->{'objects'}};
}

sub one {
  my $self = shift;
  my $filter = shift;
  return grep { $_->{'value'} == $filter } @{$self->{'objects'}}; 
}
[download]

Container's one method is returning a single Object object instead of an array reference with a single Object object inside.

The fix is quite simple:

sub one {
  my $self = shift;
  my $filter = shift;
  return [ grep { $_->{'value'} == $filter } @{$self->{'objects'}} ];
}
[download]

Output:

container=Container=HASH(0x1cc2e10)
all:

Object=HASH(0x1cdf6b0) name is foo

Object=HASH(0x1cdf788) name is bar

one:

Object=HASH(0x1cdf6b0) name is foo

Have one/all return arrayrefs, not lists?

sub all {
  my $self = shift;
  return $self->{'objects'};
}

sub one {
  my $self = shift;
  my $filter = shift;
  return [ grep { $_->{'value'} == $filter } @{$self->{'objects'}} ];
}
[download]

You're absolutely right, both of you... Damnit. Well, at least I'll be able to sleep tonight :-)

-- FloydATC

Time flies when you don't know what you're doing