boost::corosio::socket_option::v6_only

class v6_only
    : public boolean_option

void
accept_ipv6_peers_only(corosio::tcp_acceptor& acc)
{
    if (auto ec = acc.open(corosio::family::v6))
        return; // report the error

    // Set between open() and bind(): once bound, the option no longer moves.
    // Disabled, an IPv6 acceptor also accepts IPv4 peers and reports them as
    // v4-mapped addresses. tcp_acceptor::open() leaves the acceptor dual-stack
    // (v6_only false) on every backend; tcp_socket and udp_socket are the
    // opposite, their open() making an IPv6 socket v6-only. Set the option
    // explicitly whenever either behavior matters, rather than relying on a
    // default that differs by object. set_option reports failure by throwing,
    // not by returning a code.
    acc.set_option(corosio::socket_option::v6_only(true));

    if (auto ec =
            acc.bind(corosio::endpoint(corosio::ipv6_address::any(), 8080)))
        return; // report the error
    if (auto ec = acc.listen())
        return; // report the error
}