Yikes, that 's a bug(update: shows a bug in perl itself). The call to length should explicitly be passing $_, but it 's not (update: passes nothing) when it is overridden. This causes a problem with lexical $_:
$ perl5.9.4 -w
BEGIN{
*CORE::GLOBAL::length = sub (;$) {
my $arg = @_ ? $_[0] : $_;
defined($arg) ? CORE::length($arg) : undef;
}
}
$_ = "abc";
my $_;
$_ = "defghi";
print length;
__END__
3
This should print 6 whether length is overridden or not, but as is prints 3 when it is overridden.
Update: after consideration, I think this is just a natural consequence of the ;$ prototype, and should be no longer a problem with a _ prototype (when someone implements that).
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