Question

so, i have a program like this:

#!/usr/bin/perl -w  
use strict;  
foreach (@data) {  
    if($_ eq "foo") {  
        use Foo;
        process();
    }  
    if($_ eq "bar") {  
        use Bar;
        process();
    }  
...  
}

Each included module is somewhat similar, the only difference being what the process()-sub does.

#!/usr/bin/perl -w  
use strict;  
sub process {  
...  
}

My issue: the input for the main script is a (possibly long) list of things, while processing that list i get continuous “Subroutine redefined” errors (obviously). Is there any way to “un-use” a module?
Due to the fact that the library of possible “actions” to include may grow in the future, i thought this way of including modules dynamically would be the best approach. Many thanks for your help 🙂

Answer 1

As @pilcrow said, you can solve this issue quickly by using require instead of use, but, I think this is a good example where Polymorphism is to be used.

You can create a base class like:

package Processors::Base;

sub new{
  my $class = shift;
  return bless {}, $class;
}

sub process{
  die "You can only use a subclass of me";
}

1;

And then, create your processors as packages that inherit from this base package.

package Processors::Foo;

sub process{
  ... do stuff ...
}

1;

Then your code could look like:

#!/usr/bin/perl -w  
use strict;  
for my $pkg (@data) { 
    (my $path = $pkg) =~ s{::}{/}g;
    require "$path.pm";
    $pkg->process; 
    ...  
}

Of course, the modifications assume that $_ is in the form of Processors::Foo for example. Even if you can not modify the content of your @data, I think you can generate the name of the processor so that you are able to invoke its process() method.

If you want to be a show-off, you could create a Factory object that will return instances of your processors based on the value of $_:

package Processors::Factory;

sub get_instance{
  my ($self, $processor_name) = @_;

  my $full_processor_name = sprintf('Processors::%s', ucfirst($processor_name) );

  (my $full_processor_path = $full_processor_pkg) =~ s{::}{/}g;
  require "$full_processor_path.pm";

  my $processor = $full_processor_name->new();

  return $processor;
}

1;

Then, your code would look like:

#!/usr/bin/perl -w  
use strict;
use Processors::Factory;

foreach (@data) { 
    Processors::Factory->get_instance( $_ )->process();
    ...  
}