Here the solution from "Perl Hacks". It's freely downloadable from O'Reilly

package Attribute::Docstring;

use strict;
use warnings;

use Scalar::Util 'blessed';
use Attribute::Handlers;

my %doc;

sub UNIVERSAL::Doc :ATTR
{
    my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
    return if $symbol eq 'LEXICAL';

    my $name                = *{$symbol}{NAME};
    $doc{ $package }{$name} = $data;
}

sub UNIVERSAL::doc
{
    my ($self, $name) = @_;
    my $package       = blessed( $self ) || $self;

    return unless exists $doc{ $package }{ $name };
    return               $doc{ $package }{ $name };
}

1;
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application

package Counter;

use strict;
use warnings;

use Attribute::Docstring;

our $counter :Doc( 'a count of all new Foo objects' );

sub new :Doc( 'the constructor for Foo' )
{
    $counter++;
    bless {}, shift;
}

sub get_count :Doc( 'returns the count for all foo objects' )
{
    return $counter;
}

1;
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