Question

I have a module say Foo.pm

package Foo; 
sub new {
}    
sub SomeMethod {
}
1;

Then a subclass,Foo::Bar Foo/Bar.pm

package Foo::Bar;
use base Foo;
use Foo; 
sub SomeMethod {
}
1;

Now do we need to use

use base Foo;
use Foo;

or just

use base Foo;

will do both.

Also if we need to use use Foo;

What different does it do?

Answer 1

use base Module; will always load the package if needed, but it won’t import from it. It’s similar to

BEGIN {
    require Module;
    push @ISA, 'Module';
}

use Module;, on the other hand, will import the module’s default exports*. It’s similar to

BEGIN {
    require Module;
    Module->import();
}

So the use Foo; following use base 'Foo'; isn’t required unless you want to import from the module.

---

* — Technically, it merely calls import with no arguments if the module defines such a method. What I described is the normal behaviour of import methods.