use strict;

my $sub = sub {
    print "Hello!\n";
};

my $var = 'Bar';
my $pak = 'Foo::';
my $ref = \%main::;

$ref->{'Foo::'}{bar} = $sub;
$main::{'Foo::'}{$var} = $sub;
$ref->{$pak}{baz} = $sub;
$main::{$pak}{boo} = $sub;

Foo::bar();
Foo::Bar();
Foo::baz();
Foo::boo()