{
  package Container;

  use overload (
    '@{}'    => sub { return [sort keys %{$_[0]}] },
    fallback => 1,
  );

  sub new {
    return bless { map { $_ => 1 } @_[1 .. $#_] }, $_[0];
  }
}

my $c = Container->new( qw/ e1 e2 e3 / );

print "member $_\n"
  for @$c;

__output__

member e1
member e2
member e3