I've been studying the source code and can't figure out how "line" works, namely how it handles lists of two floats in the leftmost inlet. Somehow line_ft1 gets called with the second float before line_float does because I don't see any other way x_gotinlet is not zero unless I'm missing something. Thanks!

apparently the default list method unpacks the list members into the object's inlets, starting with the last and working backwards. The message forwarding is in m_class.c and then pd_defaultlist calls obj_list which actually does the unpacking

awesome, thx! yeah, it looks like obj_list in m_obj.c iterates through successive inlets in the for loop with ip = ip->i_next.