I have added another layer of bookkeeping to make it simpler to use assuming that something like HASH(0x7c2300) is a unique identifier for a hash and does not change during runtime. 

use strict;
use warnings;

sub hashIteratorFactory {
    my $h = shift;
    my @both;
    my $exhausted = 0;
    return sub {
        my $i = 0;
        return sub {
            my ($k, $v);
            if( !defined $both[$i] ) {
                if( !$exhausted and (( $k, $v ) = each %$h) ) {
                    push @both, [ $k, $v ];
                } else {
                    $exhausted = 1;
                    $i = 0;
                    return wantarray() ? () : undef();
                }
            } else {
                ( $k, $v ) = @{$both[$i]};
            }
            $i++;
            return wantarray() ? ( $k, $v ) : $k;            
        }
    }
}

my %hashIteratorStore;

sub hashIterator {
    my $h = shift;
    die "Not a hash reference!" unless ref $h eq 'HASH';
    $hashIteratorStore{$h} //= hashIteratorFactory($h);
    return $hashIteratorStore{$h}->();
}

my %h;
@h{'a'..'d'} = 1..4;
print \%h,"\n";


my %h2;
@h2{'e'..'i'} = 5..8;

my $i1 = hashIterator( \%h );
my $i2 = hashIterator( \%h );

print "1:",$i1->(),"\n";
print "1:",$i1->(),"\n";
print "2:",$i2->(),"\n";
print "1:",$i1->(),"\n";
print "1:",$i1->(),"\n";

my $i4 = hashIterator( \%h2 );

print "2:",$i2->(),"\n";
print "2:",$i2->(),"\n";
print "1:",$i1->(),"\n";

print "4:",$i4->(),"\n";
print "4:",$i4->(),"\n";

print "1:",$i1->(),"\n";
print "2:",$i2->(),"\n";
print "2:",$i2->(),"\n";

my $i3 = hashIterator( \%h );
while( my ($k, $v) = $i3->() ) {
    print "3:$k$v\n";
}

print "2:",$i2->(),"\n";
print "1:",$i1->(),"\n";

[download]

This is really only a starting point as it is really read-only. If the hash is changed somewhere inbetween, the cached keys and values will be unmodified. So more work is required.

In reply to Re^3: Indepedent lazy iterators for the same hash? by hdb
in thread Indepedent lazy iterators for the same hash? by LanX

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