void set_chain(chain_type* c)
{ chain_ = c; chain_->register_client(this); }
#if !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) && \
void set_chain(chain_type* c)
{ chain_ = c; chain_->register_client(this); }
#if !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) && \