http://qs1969.pair.com?node_id=1150139


in reply to Re^3: Declaring with my, assigning, and testing in same line (attributes)
in thread Declaring with my, assigning, and testing in same line

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;
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