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

Before I go re-invent the wheel, does anyone know of a module/snippet that will take a scalar (reference or not) and return a copy of it? This doesn't sound so hard, but I want to copy anything within it, so a hash of lists of hashes, when copied, should make a copy of the hash. That new hashref should point to listrefs that are different than the original's. And, those listrefs should point to hashrefs that have been copied, as well.

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Re: Recursive copier
by btrott (Parson) on Jun 18, 2001 at 21:48 UTC
    You could get the effect of a deep copy by serializing and deserializing a data structure, using some method of serialization. Eg. Data::Dumper or Storable.

    Or you could also investigate the Clone module, which I've not seen before but which is on CPAN. It looks like it should do what you want: 

        use Clone qw(clone);
    my $b = clone($a);

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Re: Recursive copier
by extremely (Priest) on Jun 19, 2001 at 01:26 UTC
    Best way, period, is: 
    use Storable qw(dclone);
# Deep (recursive) cloning
$cloneref = dclone($ref);

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    Keeping in mind it is shipped for free with any fairly modern perl installation (INST_FILE /usr/local/lib/perl5/site_perl/5.6.0/i686-linux/Storable.pm) and is one of the more regularly "use"d modules in other modules. That means the perl-porters themselves have taken a modicum of interest in seeing that it is correct and complete.

    The likelyhood is, you already have Storable installed!

    --
    $you = new YOU;
    honk() if $you->love(perl)

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Re: Recursive copier
by dimmesdale (Friar) on Jun 18, 2001 at 21:39 UTC
    {I hope this works; it appears PM is having problems today; my browser keeps saying that the page doesn't exist}

    Well, what you are saying sounds familiar(in C/C++ it happens a lot w/ classes, and is called shallow vs. deep copying). I don't know of any modules that have this, but I can give you some advice:

    (1)Recursive is definately the way to go
    (2)Make variables lexically scoped, i.e., with *my*; perl won't delete these variables if there's a ref. to them, but if the funtion's called again(e.g., recursively) it'll create a new copy of them
    (3)Post your code here if you have any problems

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Re: Recursive copier
by DrZaius (Monk) on Jun 18, 2001 at 22:29 UTC
    Hehe, after a comment from btrott and a cold shower I realized I answered the wrong question. Oh well :) You probably don't need recursion in your algo if you use a File::Copy/File::Find combo like this: 
    use strict;
use File::Copy qw/copy/;
use File::find qw/find/;

sub rcopy {
 my $src = shift;
 my $dst = shift;

 find(sub {
  my ($src_file, $dst_file) =
    ($File::Find::fullname, $File::Find::fullname);

  $dst_file =~ s!^$src!$dst!;
  copy $src_file, $dst_file
   or die "Could not copy $src_file => $dst_file:$!";
 }, $src);
}

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