package Foo;
use strict;
use warnings;
#...

my %cache;
sub fetch {
  my $class = shift;
  my $instance = shift;
  return $cache{$instance} if $cache{$instance};

  my $self = {};
  bless ($self, $class);
  $cache{$instance} = $self;

  $self->{name} = $instance;
  # more initialisation.
  $self;
}