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;
    }

}