You can tie in the attribute handler, so you can untie there, too. So, a closure sent as an extra argument to the constructor works:
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
{ package Array::Nonempty::Attr;
use Attribute::Handlers;
sub Nonempty :ATTR(ARRAY) {
my $referer = $_[2];
tie @$referer, 'Array::Nonempty', sub { untie @$referer }
}
}
{ package Array::Nonempty;
use Tie::Array;
use parent -norequire => 'Tie::StdArray';
use Carp;
sub CLEAR {
my $self = shift;
$self->[0] = [];
}
sub TIEARRAY {
my ($class, $untie) = @_;
bless [ [], $untie ], $class
}
sub EXTEND {
my ($self, $size) = @_;
croak "Cannot be empty" if 0 == @{ $self->[0] } && 0 == $size;
$self->SUPER::EXTEND($size);
# Prevent "untie attempted while 1 inner references still exis
+t"
my $untie = $self->[1];
undef $self;
$untie->()
}
}
use parent -norequire => 'Array::Nonempty::Attr';
my %hash_ok = ( answer => 42 );
my %hash_empty = ();
my @keys_ok :Nonempty = keys %hash_ok;
say tied(@keys_ok) // 'not tied';
say for @keys_ok;
my @keys_empty :Nonempty = keys %hash_empty;
($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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