How to create a module-global internal variable in Perl?

Question

I want to create a static variable in my module. How can I do that? Can I use our or state ?

Here is an example of what I want to achieve:

use MyModule;
MyModule::increase_count(); # should return 0
MyModule::increase_count(); # should return 1
MyModule::increase_count(); # should return 2

Answer 1

If you want to use state (which is a good idea):

package MyModule;

# return the previous value
sub increase_count {
  state $count = 0;
  return $count++;
}

Using state minimizes the visibility of the symbol. If you have to share the visibility accross multiple subs, you can enclose a lexical variable in a block:

{
  my $count = 0;
  sub increase_count { $count++ }
  sub current_count  { $count   }
  sub decrease_count { $count-- }
}

Answer 2

If you want to access $counter variable directly outside of MyModule package, use our , but if you don't then my is what should be used,

package MyModule;

my $counter = 0;
sub increase_count {

  return $counter++;
}