This is no longer in answer to you initial question, as dbp pointed out that Date::Calc does not provide an object interface, but I got curious as to what happens when you call a method on something that is not an object. Lessee...

#!/usr/local/bin/perl -w

use strict;
package Test;
print Test->method();
sub method {
  my $self=shift;
  return $self;
}
__END__
Test
[download]

Ah, that's right - you get the package name. I knew this ;).

So that answers your question: if no object has been created, calling a function with -> results in the function getting the package name as the first argument. This also explains the error in your script: Date::Calc::Add_Delta_Days gets 'Date::Calc' as the year, hence the usage message.

Update: See bart's post below for some more information on -> syntax.

CU
Robartes-