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

Hi, monks!

I'm wondering if some of you know if exists an effective trick for copying a hash. I mean, does exists some method that allows to duplicate a hash or an array, entirely, creating new references when necessary (not copying the references)? ... (difficult to explain ...)

For example, if i have this array: 

@a = ([1,2,3],[a,b,c]);

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Which is compossed by two references to other arrays (ARRAY(0x814cc20), ARRAY(0x819eae0)) p.e.
I want to make a new copy of that array, and a new copy of each sub-element referenced, with the same content. 
(ARRAY(0x814aaaa), ARRAY(0x819bbbb))

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Dumping the element to a file, and re-reading is the only way? ... or does it copy the references to a file, so when you load it, perl can allocate the elements on the same memory position? ...
In c++, for make a copy of an object programmers must implement the copy constructor ... I think, i can do the same in perl (with little problems like, how can I allocate new memory, or how can I make the same as memcpy ... bad habits ^_^>), but after, i've saw the power of the Dumpvalue module ... i cant think in other way to do it ...

Thanks, :-)

turo

perl -Te 'print map { chr((ord)-((10,20,2,7)[$i++])) } split //,"turo"'

Replies are listed 'Best First'.
Re: Dump, Dup or Copy an object
by holli (Abbot) on Feb 22, 2006 at 13:13 UTC
    What you want is called a "deep copy" or "clone". See my node here for some modules that apply here.

    Update:
    You might also want to have a look at Class::Cloneable if your structure is actually an object.


    holli, /regexed monk/
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[d/l]
Re: Dump, Dup or Copy an object
by borisz (Canon) on Feb 22, 2006 at 13:33 UTC
    My choice would be Storable's dclone function.
    Boris
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      map {thanks} qw(arkturuz borisz holli);

      The Storable module is what i need (i think so, after reading the pod): 

      # Deep (recursive) cloning
$cloneref = dclone($ref);

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      ummm, The Class::Cloneable, is cool, but remembers me c++ and the copy constructor, maybe i'll consider to use it soon ... :-) .
      And, at last the powerfull Data::Dumper is too complex, i suppose, for what i wantted to do (indeed, i don't know what to do with it ^_^> ... by the momment), ...

      Cheers

      perl -Te 'print map { chr((ord)-((10,20,2,7)[$i++])) } split //,"turo"'
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[d/l]
[select]
        Out of curiosity i benchmarked it and got the following results: 
        use Benchmark qw(timethese);

use Clone;
use Storable;
#use Scalar::Util::Clone;

my $struct = { 'foo' => 'bar', 'move' => 'zig', bar => [1, 2, 3] };

timethese
(
    500000,
    {
        'Clone'               => sub { my $s = Clone::clone($struct)  
+              },
        #'Scalar::Util::Clone' => sub { my $s = Scalar::Util::Clone::c
+lone ($struct) },
        'Storable'            => sub { my $s = Storable::dclone ($stru
+ct)           }
    }
);

#Benchmark: timing 500000 iterations of Clone, Storable...
#  Clone:  3 wallclock secs ( 4.28 usr +  0.00 sys =  4.28 CPU) @ 1169
+04.37/s (n=500000)
#  Storable: 74 wallclock secs (69.62 usr +  0.03 sys = 69.65 CPU) @ 7
+178.65/s (n=500000)

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        The reason because Scalar::Util::Clone is commented out is that I couldn't make it compile nor did I find a ppd for it. Maybe someone else can step in?


        holli, /regexed monk/
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[d/l]
      Dumping the element to a file, and re-reading is the only way?
      The OP is already aware of Data::Dumper.

      Update: Sorry Boris, my bad. This was of course meant to be a reply to arkturuz' node above.


      holli, /regexed monk/
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        ???
        Boris
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Re: Dump, Dup or Copy an object
by arkturuz (Curate) on Feb 22, 2006 at 13:23 UTC
[reply]

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