Re^3: ref to read-only alias ... why? (not consistent)

[LanX]

Your right it's not consistent.

But IMHO consistency will most likely break legacy code.

I think that there should at least be a warning.

Since it's not always clear if a variable is an alias, this can cause very hard to detect errors in subs which are meant to modify call-by-reference parameters. (not to be confused with Perl references)

Did you check if there are already older bug-reports regarding this?

UPDATE:

  DB<108> sub inc_a { $_[0]++; return }
 
  DB<109> $x=1; inc_a($x); print $x
2
  DB<110> inc_a(1)
Modification of a read-only value attempted at (eval 13)[/usr/share/pe
+rl/5.10/perl5db.pl:638] line 2.

but

  DB<111> sub inc_b { my $r=\ $_[0]; $$r++; return }
 
  DB<112> $x=1; inc_b($x); print $x
2
  DB<113> inc_b(1)
 
  DB<114>

When passing an aliasing variable instead of 1 it's the same problem. With inc_b non-aliasing vars will increment, but aliases will silently fail to increment.