Difference between use Modulename; and use Modulename();

Question

Is there any difference between use Modulename; and use Modulename(); ? Sometimes I see, for example, use Carp; and sometimes use Carp ();

Answer 1

As documented,

use Modulename;

is the basically the same as

BEGIN {
   require Modulename;
   import Modulename;
}

while

use Modulename ();

is the basically the same as

BEGIN { require Modulename; }

That means the parens specify that you don't want to import anything. (It would also prevent a pragma from doing its work.)

---

Carp exports confess, croak and carp by default, so

use Carp;

is short for

use Carp qw( confess croak carp );

By using

use Carp ();   # or: use Carp qw( );

confess, croak and carp won't be added to the caller's namespace. They will still be available through their fully qualified name.

use Carp ();
Carp::croak(...);

Answer 2

Without the (), the package's import method will be called, possibly causing some default set of names to be exported into the calling package's namespace.

Passing the () explicitly says "Do not import any names into my namespace."

Most modern object-oriented modules don't export anything by default anyway, and there's nothing stopping them from manually polluting the caller's namespace if they wanted to, but specifying () is a signal that you're not relying on names magically appearing just because you imported a package.