#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @array = (
    {a => 'b'},
    {1 => 2},
    {1 => 2},
);

my %seen;
my @unique = map{ $_->[0] }grep{ !$seen{$_->[1]}++ }map{ [$_,flatten($_)] }@array;
print Dumper \@unique;

sub flatten{
   my ($hashref) = @_;
   my $string = '';
   
   while( my ($key,$val) = each %$hashref ){
      $string .= $key . '_::_' . $val . '_::_';
   }

   return $string;
}