Let's say I want to use Tie::Hash to have a temporary wrapper around an existent hash until I untie.

In the following example I'm simply returning any value enclosed in < > .

I'm facing some "complications", which make me doubt I'm doing the right thing.

• to access the original data I have to pass the hash-ref again to the constructor, there doesn't seem to be any reverse tied command helping here, so I need to explicitly store it in the object. °
• When internally accessing the data of the original hash, I have to explicitly untie and retie the hash again, otherwise I'm causing an infinite recursion (yikes)
• I'm getting an untie attempted while 1 inner references still exist unless I undef the object prior, I'm not sure what this warning is supposed to mean. And it only cares about other refs in the same scope. SEE UPDATE ²

I'm sure I could kind of avoid all this by copying all data of the original hash when constructing the tie inside TIEHASH, but this seems like a waste of resources.

Any more elegant approach???

use v5.12;
use warnings;


package main;

my %hash;
@hash{"a".."c"} = 40 ..42;              # init

tie                                     # bind wrapper
  %hash,
  'Data::Proxy::TieHash',
  \%hash;                               # redundant, why?

say $hash{a};

say @hash{"a".."c"};

delete $hash{b};

say @hash{"a".."c"};

untie %hash;                            # unbind wrapper

say @hash{"a".."c"};


BEGIN {
    package Data::Proxy::TieHash;
    require Tie::Hash;
    use Scalar::Util qw/blessed/;

    use Carp;
    our @ISA = qw(Tie::ExtraHash);

    # All methods provided by default, define 
    # only those needing overrides
    # Accessors access the storage in %{$_[0][0]};
    # TIEHASH should return an array reference with the first element
    # being the reference to the actual storage

    sub _report {
        #  uncomment to trace
        #carp "Doing \U$_[0]\E of $_[1] at $_[2].\n"
    };

    sub DELETE {
        my ($obj, $key) = @_;
        my ($meta, $orig) =@$obj;
        _report('DELETE', $orig, $key);

        my $class = blessed $obj;
        undef $obj;
        untie %{$orig};
        my $ret = delete $orig->{$key};
        tie %{$orig}, $class, $orig;
        return $ret;
    }

    sub FETCH {
        goto &FETCH1;                   # use implementation
    }

    sub FETCH0 {
        _report('FETCH', $_[0][1], $_[1]); 

        untie %{$_[0][1]};
        my $ret = $_[0][1]->{$_[1]};
        tie %{$_[0][1]}, 'Data::Proxy::TieHash', $_[0][1];
        return "<$ret>" if defined $ret;
        return undef;
    }


    sub FETCH1 {
        my ($obj, $key) = @_;
        my ($meta, $orig) =@$obj;

        _report('FETCH', $orig, $key);

        my $class = blessed $obj;
        undef $obj;                     # avoid warning
        untie %{$orig};
        my $ret = $orig->{$key};
        tie %{$orig}, $class, $orig;
        return "<$ret>" if defined $ret;
        return undef;
    }

}
[download]

<40>
<40><41><42>
Use of uninitialized value in say at proxy_tiehash.pl line 21.
<40><42>
Use of uninitialized value in say at proxy_tiehash.pl line 25.
4042
[download]

UPDATES

°) this smells like internally causing a recursive data structure

²) OK I got it https://perldoc.perl.org/perltie#The-untie-Gotcha, untie is normally supposed to trigger DESTROY, but inf there are still other refs to the underlying $object DESTROY can't be triggered. In my case it's actually better not to trigger DESTROY and better to silence the warning altogether.

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.