Read-only result? I'm not sure what you mean by that, but if you assign to an element of $r, that affects $my_hash_ref. They're all references so they're pointing at the same data.

#!/usr/bin/perl

use Data::Dumper;

my $hash = {
    a => { ab => { ac => 'fred' }, abb => 'barney' },
    b => 'betty',
    c => { cb => 'dino' },
    };

my $r = $hash;

my @k = qw( a ab );

print Dumper( $hash );

$r = $r->{$_} foreach @k;

$r->{ 'ac' } = 'Mr. Slate';

print Dumper( $hash );
[download]

You didn't change $r the accessed value in your snippet — you changed that which is pointed by $r — so you failed to disprove that $r the accessed value is read-only.

Say you want to do $my_hash_ref->{$k[0]}->{$k[1]}->{$k[2]} = 3;. Compare

use Data::Dumper;

my $my_hash_ref = { a => { b => { c => 2 } } };

my @k = qw( a b c );

my $r = $my_hash_ref;
$r = $r->{$_} foreach @k;
$r = 3;

print Dumper($my_hash_ref);
# { 'a' => { 'b' => { 'c' => 2 } } };
[download]

with

use Data::Dumper;

my $my_hash_ref = { a => { b => { c => 2 } } };

my @k = qw( a b c );

my $p = \$my_hash_ref;
$p = \($$p->{$_}) foreach @k;
$$p = 3;

print Dumper($my_hash_ref);
# { 'a' => { 'b' => { 'c' => 3 } } };
[download]

Update: Fixed a terminology error.

Perhaps you could define "read-only", because I can certainly change $r. I can just assign it a new value. I can change the data it points to. None of those things relate to "read-only". It's the conpletely wrong way to think about it.

That $r no longer is a reference when I give it another value doesn't really matter.

--
brian d foy <brian@stonehenge.com>
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