use Tie::OneOff;

{
	my $i;
	sub int_only() : lvalue {
		+Tie::OneOff->lvalue({
			STORE => sub { $i = ($_[0] =~ m/^\d+$/s) ? $_[0] : die "bad int" },
			FETCH => sub { $i },
		})
	};
}

use Test::More 'no_plan';
use Test::Exception;

lives_ok { int_only = 42 } 'can set int_only to be an integer';
is int_only, 42, 'value set okay';

dies_ok { int_only = "a" } 'cannot set it to be a non-int';
is int_only, 42, 'old value preserved';

int_only =~ s/42/24/s;
is int_only, 24, 'substitution works';

dies_ok {int_only =~ s/4/a/s } 'cannot replace number with letter';