From jrahmeh@pyxistech.com

1. Rakudo version​:
  This is Rakudo Perl 6, version built on parrot 2.7.0 r48768

2. Code that caused the bug​:
  sub incr3 (*@​v is rw) { for @​v -> $x { $x++} }
  my ($a, $b) = (0, 0);
  incr3($a, $b);
  say "incr3​: $a, $b";

3. Output​:
  Cannot modify readonly value
  in '&infix​:<=>' at line 1
  in <anon> at line 7071​:CORE.setting
  in 'incr3' at line 1
  in main program body at line 3​:a3.1

4. Expected behavior​: Code should have compiled without any errors
  It should have produced following output​:
  incr3​: 1 1

From jrahmeh@pyxistech.com

1. Rakudo version​:
  This is Rakudo Perl 6, version built on parrot 2.7.0 r48768

2. Code that caused the bug​:
  sub incr1 (*@​v is rw) { @​v[0]++; @​v[1]++; }
  sub incr2 (*@​v is rw) { for @​v { $_++} }

  my ($a, $b) = (0, 0);
  incr1($a, $b);
  say "incr1​: $a, $b";

  ($a, $b) = (0, 0);
  incr2($a, $b);
  say "incr2​: $a, $b";

3. Output​:
  incr1​: 0, 0
  incr2​: 1, 1

4. Expected output​:
  incr1​: 1, 1
  incr2​: 1, 1

From @qiuhw

  于 2010年09月09日 03​:44, Joe Rahmeh (via RT) 写道​:

# New Ticket Created by Joe Rahmeh
# Please include the string​: [perl #​77738]
# in the subject line of all future correspondence about this issue.
#<URL​: http://rt.perl.org/rt3/Ticket/Display.html?id=77738>

1. Rakudo version​:
This is Rakudo Perl 6, version built on parrot 2.7.0 r48768

2. Code that caused the bug​:
sub incr3 (*@​v is rw) { for @​v -> $x { $x++} }
I think you should write this line as this​:
sub incr3 (*@​v is rw) { for @​v -> $x is rw { $x++ } }
my ($a, $b) = (0, 0);
incr3($a, $b);
say "incr3​: $a, $b";

3. Output​:
Cannot modify readonly value
in '&infix​:<=>' at line 1
in<anon> at line 7071​:CORE.setting
in 'incr3' at line 1
in main program body at line 3​:a3.1

4. Expected behavior​: Code should have compiled without any errors
It should have produced following output​:
incr3​: 1 1

The RT System itself - Status changed from 'new' to 'open'

From @coke

On Wed Sep 08 12​:46​:36 2010, jrahmeh@​pyxistech.com wrote​:

1. Rakudo version​:
This is Rakudo Perl 6, version built on parrot 2.7.0 r48768

2. Code that caused the bug​:
sub incr1 (*@​v is rw) { @​v[0]++; @​v[1]++; }
sub incr2 (*@​v is rw) { for @​v { $_++} }

my \($a, $b\) = \(0, 0\);
incr1\($a, $b\);
say "incr1​: $a, $b";

\($a, $b\) = \(0, 0\);
incr2\($a, $b\);
say "incr2​: $a, $b";

3. Output​:
incr1​: 0, 0
incr2​: 1, 1

4. Expected output​:
incr1​: 1, 1
incr2​: 1, 1

Current output​:

incr1​: 0, 0
incr2​: 0, 0

--
Will "Coke" Coleda

The RT System itself - Status changed from 'new' to 'open'

From @usev6

This works now​:

sub incr1 (*@​v is rw) { @​v[0]++; @​v[1]++; }; my ($a, $b) = (0, 0); incr1($a, $b); say "incr1​: $a, $b";
incr1​: 1, 1

sub incr2 (*@​v is rw) { for @​v { $_++} }; my ($a, $b) = (0, 0); incr2($a, $b); say "incr2​: $a, $b";
incr2​: 1, 1

sub incr3 (*@​v is rw) { for @​v -> $x is rw { $x++ } }; my ($a, $b) = (0, 0); incr3($a, $b); say "incr3​: $a, $b";
incr3​: 1, 1

sub incr3_old (*@​v is rw) { for @​v -> $x { $x++} }; my ($a, $b) = (0, 0); incr3_old($a, $b); say "incr3_old​: $a, $b";
Cannot assign to a readonly variable or a value

I added tests to S04-statements/for.t with the following commit​: Raku/roast@c58e1975f5

@usev6 - Status changed from 'open' to 'resolved'