I meant that both of the potential fixes for this feel unnatural:
  1. using s/(x)/fn "$1"/e (with quotes around $1), or
  2. using what you suggested: (my $new = $old)... or any other form of that.
Both fixes require an extraordinary amount of coupling between the caller and the function. Either:
  1. the caller needs to know that the argument to fn() will be used directly from @_ after a regexp, or
  2. the function needs to know that the argument is an alias of a global variable which will be modified by the regexp.
Only if they have this tight coupling does it make sense to use either of these two precautions to avoid the issue I ran into.

I think the takeaway for me is that when passing $1, etc into a function, that it should be quoted (to copy it), even though the general rule is when passing a variable $var into a function, (almost) never should it be quoted, as in fn("$var"). This feels exactly like the kind of kludgy rules you have to remember to use C++ "correctly".

In reply to Re^4: Strange modification of @_ by jrw
in thread Strange modification of @_ by jrw

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