Wow. That piece of enlightenment gives me hope that someday I might be able to use the perl debugger with unicode data... I've had repeated failures when using "perl -d" on scripts that involve regex operations on utf8 strings, in 5.8.6 on macosx and 5.8.7 on freebsd. A script would run okay by itself (except for bugs), but running it with "perl -d" leads to various reports of "out of memory" at the first unicode-heavy regex. So, I'm guessing the debugger contains something similar to the logic you've cited in Carp::Heavy. (But curiously, I can run a one-liner applying that regex to a utf8 string on my mac without difficulty. I'm confused.)

Anyway, I can't say that I approve of the approach taken in that patch. All it's doing is: if the string has the utf8 flag on, avoid trying to make any non-visible or non-ascii characters "displayable" by converting them to hex notation.

Rather than just give up completely on utf8 strings, wouldn't it be better to use a different approach? e.g.:

$arg = join "", 
       map {
             ($_ lt ' ' or $_ gt '~') ? sprintf("\\x{%x}",ord) : $_ 
           } split //, $arg;
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I'm not sure, but I think that should avoid the malloc explosion caused by using [[:cntrl:]]|[[:^ascii:]] on a utf8 string.