Thanks for your detailed answer! By the way, as your replied on this , 5.30 will add named parameter. I'm curious if it would affect current mechanism of argument stack which you mentioned above?
That's no longer likely to happen for 5.30: I ran out of time. Named sub parameters will only affect the sub itself, not the caller; and named args will only apply to perl subs, not to XS subs.

Dave.

In reply to Re^5: what definition of Istack_sp by dave_the_m
in thread what definition of Istack_sp by xiaoyafeng

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