I discovered a side-effect of this new feature that does not appear to be documented, well lets say I can't find it anyway. I don't think this has been discussed before, apologies if that is wrong.

$_ appears to be passed by reference. If you alter $_ in the subroutine then it alters (or attempts to alter) the caller's $_.
sub mysub (_) {
    s/o/u/g;
}

for (qw(The quick brown fox)) {
   mysub()
}

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Gives Modification of a read-only value attempted which I can see might catch some people out. The fix is to defined $_ as a 'my' variable, but that rather defeats the object.

This is consistent with altering @_ elements. As the reader probably knows, altering @_ as a whole does not alter the caller's arguments, but altering, for example, $_[0] does.

I know I am probably the only one here that thinks prototypes can be useful (can), and I know what TheDamian thinks of them.

In reply to Underscore _ prototype in 5.10 by cdarke

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