apackage.pm:
use strict;

sub process1 {
    print "abcd\n";
}

1;

test1.pl:
my $a = \&process1;#process1 does not exist at this moment
print $a, "\n";
require apackage;#process1 is realized. If you comment out this, there would be an error when you call process1 later.
print $a, "\n";
&$a;