> So what's the take-away here? If your sub has to put stuff in variables outside its own scope, don't also pass those variables as parameters?

It's even more complicated.

You could call another sub (which calls another sub) which is deleting elements from the closure before accessing @_.

I think the rule of thumb is

• always try to copy @_ first and avoid accessing any $_[n] afterwards.
• if you really need the aliasing effect or high performance, be sure to avoid side effects by calling unknown functions or even directly overwriting closed over vars.

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