Here's a base class for generating flattened accessors for nested hash structs:

package Class::StructAccessors;
use warnings; use strict;

use Scalar::Util qw/reftype/;

sub mk_struct_accessors {
    my ($class, $struct, $path, $key_seen, $ref_seen) = @_;

    $path ||= [];
    $key_seen ||= {};
    $ref_seen ||= {};

    while (my ($k,$v) = each %$struct) {

        my $reftype = reftype($v)||'';
        
        if ($reftype) {
            die "Bad reference type: $reftype"
                unless ($reftype eq 'HASH');
                
            die "Cycle detected at $v"
                if ($ref_seen->{$v});
                
            $ref_seen->{$v} = 1;
            
            $class->mk_struct_accessors($v, [@$path, $k], $key_seen, $
+ref_seen); 
        }
        else {
            die "null key" unless (defined $v && $v ne '');

            die "Duplicate key detected $v"
                if ($key_seen->{$v});
                
            $key_seen->{$v} = 1;
            #
            # add this accessor to the class
            #
            no strict 'refs';
            warn "adding: $v";

            *$v = sub {
                my $self = shift;
                return $self->_dereference(@$path, $k, $v);
            }
       }
  }
}

sub _dereference {
    my $self = shift;
    my @hash_keys = @_;

    my $ref = $self;

    while (@hash_keys && $ref) {
        
        $ref = $ref->{shift(@hash_keys)};
    }
    return $ref;
}

1;
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It dies if the struct contains any duplicate keys or cycles.

A test script follows:

package Foo;
use base qw{Class::StructAccessors};
 
__PACKAGE__->mk_struct_accessors({
   A => {
      B => 'C'
   },
   D => {
      E => {
         F => 'G'
      }
   },
##   Z => 'G', # Duplicate test
##   X => [1,2,3], # Bad type test
##   N => do {my $cycle = {}; $cycle->{M} = $cycle; $cycle;}, # Cyclic
+ test
});

package main;
use Foo;

my $obj = bless {
   A => {
      B => {'C' => "It's hello from C"},
   },
   D => {
      E => {
         F => {'G' => "G'day from G"}
      }
   }
}, 'Foo';

print "C:".$obj->C."\n";
print "G:".$obj->G."\n";
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Update: Added test for cycles.