package Grand::Parent;
use strict;
use warnings;

sub new {
    my $class = shift;
    return { struct => $class->STRUCT };
}
# ---------------------------------
package Grand::Parent::Child;
use strict;
use warnings;
use base qw(Grand::Parent);

sub STRUCT {
    { key => "value" }
}
# ---------------------------------
package main;
use strict;
use warnings;

my $child = Grand::Parent::Child->new();
print $child->{struct}->{key};