deep copy of hash of hash

cmic has asked for the wisdom of the Perl Monks concerning the following question:

I thought deep copy of hash of hash would work, but when I modify the originla hash %x, the deep copy %y is modified too. What do i did wrong ?

my %x= ('miller'=> {'lastname' => 'michael','tel'=>'222'},
        'duran' => {'lastname'=> 'peggy', 'tel' => '333'},
    );

print "--Original hash \n";
for my $nom  (keys %x) {
    print "nom: ", $nom, " ";
    for my $val (keys %{$x{$nom}} ) {
        print $val, ": ", $x{$nom}{$val}, " ";
    }
    print"\n";
}
my $y= {%x};  #anonymous hash ref containg data freom %x
#
#modifying $x shouldn't affects $y ??
#
$x{'duran'}{'tel'}='888';

print "--Deep copy of Original hash \n";
#notice how to dereference $y !!
for my $nom (keys (%$y)) {
    print "nom: ", $nom, " ";
    for my $val (keys %{@$y{$nom}}) {
        print $val, ": ", $y->{$nom}{$val}, " ";
    }
    print "\n";
}

</h3>
[download]

And the code prints this (unexpected) :

--Original hash
nom: miller lastname: michael tel: 222
nom: duran tel: 333 lastname: peggy
--Deep copy of Original hash
nom: duran tel: 888 lastname: peggy
nom: miller lastname: michael tel: 222
[download]

Replies are listed 'Best First'.
Re: deep copy of hash of hash by haukex (Archbishop) on May 24, 2019 at 16:57 UTC
`my $y = {%x};` Although this does create a reference to a new anonymous hash and copies the key/value pairs (you can modify the keys of `%$y` without affecting the set of keys in `%x`), this is still not a deep copy - the values are still references to the same nested hashes (`{'lastname' => 'michael','tel'=>'222'}`) as in the original data structure. For true deep copies, see e.g. `dclone` from Storable or Clone. Minor improvements to wording.	[reply] [d/l] [select]
Re^2: deep copy of hash of hash by cmic (Acolyte) on May 27, 2019 at 09:25 UTC
I get it. However, I loaded CPAN Clone module, but as I `use Clone 'Clone'; #or even: use Clone::More qw( clone );` [download] Perl -c answers: "Clone" is not exported by the Clone module What should I do? (sorry to be a bit noob there...) TYA -- cmic. Life helps. Perl Too.	[reply] [d/l]
Re^3: deep copy of hash of hash by hippo (Bishop) on May 27, 2019 at 10:07 UTC
Perl is case sensitive. Here is an SSCCE: `use strict; use warnings; use Test::More tests => 2; use Clone 'clone'; my %x = ( miller => {lastname => 'michael', tel => '222'}, duran => {lastname => 'peggy', tel => '333'}, ); my %y = %{clone (\%x)}; is_deeply (\%x, \%y); $x{duran}{tel} = '444'; isnt ($x{duran}{tel}, $y{duran}{tel});` [download]	[reply] [d/l]
Re^3: deep copy of hash of hash by johngg (Canon) on May 27, 2019 at 09:34 UTC
The documentation says `Use Clone 'clone';` (note the lower case) but you have asked to import `Clone` with an initial upper case letter. I can't test as I don't have that module but perhaps that is your problem. Cheers, JohnGG	[reply] [d/l] [select]


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