in reply to %+ and cloning

Try this version of your code that uses Data::Dump and things become obvious: 

#! perl -slw
use strict;
use warnings;
use Storable qw(dclone);
use Data::Dump qw[ pp ];

my $str = "Rico";

$str =~ m{(?<name>ico)}xms;

my $match = dclone \%+;

print \%+,;
print " match:  $match -",  pp $match;

$str =~ m{(?<buba>R)}xms;

my $match2 = dclone \%+;

print \%+;

print " match:  $match ",  pp $match;
print "match2: $match2 ",  pp $match2;

__END__
C:\test>816700
HASH(0x22ee20)
 match:  HASH(0x6f218) -{
  # tied Tie::Hash::NamedCapture
}
HASH(0x22ee20)
 match:  HASH(0x6f218) {
  # tied Tie::Hash::NamedCapture
}
match2: HASH(0x6f128) {
  # tied Tie::Hash::NamedCapture
}

[download]

%+ is not a real hash, but rather a tied hash. And cloning it appears to simply gives you another tied reference to the same global internal data structure.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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Replies are listed 'Best First'.
Re^2: %+ and cloning
by PetaMem (Priest) on Jan 11, 2010 at 12:30 UTC

    Thanks for your insight.

    So I went back to twig technology and copied the hash via 
    sub copy_hash {
    my $hr = shift // return {}; # get hash to copy or return empty ha
+shref if not given

    my %copy = ();

    while (my ($k, $v) = each %{$hr}) {
        $copy{$k} = $v;
    }

    return \%copy;
}

    [download]

    Which works. So this is it? Best way to go?

    Bye
     PetaMem         All Perl:   MT, NLP, NLU

[reply]
[d/l]

      A simple my %copy = %+; is equivalent to your sub. However, that may not be enough!

      According to the docs for Tie::Hash::NamedCapture, the values of the tied hash can contain an array reference holding multiple captures due to the re-use of the same named capture. In which case you might need to use something more complex to perform a deep copy operation.

      That said, in my simple tests, this doesn't seem to apply to %+. It does apply to %- though.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
[select]
        It happens if the tie happens with parameters all => 1, but %+ is tied without them. So even if your tests were less simple, you shouldn't have seen it with %+ (and if you ever do, there's a bug).
[reply]
[d/l]
[select]
      That depends on ones definition of 'best'. One could also write: 
      sub copy_hash {
    my $hr = shift // return {};
    my $copy;
    @$copy{keys %$hr} = value %$hr;
    $copy;
}

      [download]
      or just: 
      sub copy_hash {{%{$_[0]//{}}}}

      [download]
      Or without a sub: 
      my %copy = %+;

      [download]
[reply]
[d/l]
[select]

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