package C;

sub new {
    my $self = shift;
    my $class = ref($self) || $self;

    return bless {sub_ref => shift}, $class;
}

sub doit {
    $_[0]->{sub_ref}();

    # you don't always need a reference to call outside of an object
    main::hello();
}

package main;

sub hello {
    print "hello\n";
}

C->new(\&hello)->doit;