sub foo { print "foo: ", $_[0], "\n" }

&foo( 'called with &' );
foo( 'called with no &' );

my $foo_ref = \&foo;
$foo_ref->( 'called via reference' );
&$foo_ref( 'called via & and reference' );
__END__
foo: called with &
foo: called with no &
foo: called via reference
foo: called via & and reference