Re^3: I have a hash in a hash in a .....

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.

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Re^4: I have a hash in a hash in a ..... by brian_d_foy (Abbot) on Feb 21, 2006 at 20:50 UTC
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> Subscribe to The Perl Review	[reply] [d/l]
Re^5: I have a hash in a hash in a ..... by ikegami (Patriarch) on Feb 21, 2006 at 20:57 UTC
I said the result was read-only. I never said `$r` was read-only. Oops, I didn't original post, but I did in my second post. Fixed. The OP wanted a means of accessing the value at "key" @k. Using the "$r" method, one cannot edit the accessed value. Using the "$p" method, one can edit the accessed value. When something cannot be edited, it is said to be read-only. So while the scalar `$r` itself is not read-only, the accessed value is read-only. Update: Added underlined text.	[reply] [d/l] [select]