From @zoffixznet

#Doesn't work​:
<TestNinja> m​: class { has int $!n = 0; method x ($!n) {} }.new.x​: 42
<camelia> rakudo-moar 2c95f7​: OUTPUT«Cannot modify an immutable int␤ in method x at <tmp> line 1␤ in block <unit> at <tmp> line 1␤␤»

# But does, if we use a temp var​:
<TestNinja> m​: class { has int $!n = 0; method x ($n) {$!n = $n} }.new.x​: 42
<camelia> rakudo-moar 2c95f7​: ( no output )

From @lizmat

This is a known issue, as there is no native support for attribute binding this way. There’s quite some code in the setting working around this issue :-(

On 15 Sep 2016, at 20​:49, Zoffix Znet (via RT) <perl6-bugs-followup@​perl.org> wrote​:

# New Ticket Created by Zoffix Znet
# Please include the string​: [perl #​129278]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl6/Ticket/Display.html?id=129278 >

#Doesn't work​:
<TestNinja> m​: class { has int $!n = 0; method x ($!n) {} }.new.x​: 42
<camelia> rakudo-moar 2c95f7​: OUTPUT«Cannot modify an immutable int␤ in method x at <tmp> line 1␤ in block <unit> at <tmp> line 1␤␤»

# But does, if we use a temp var​:
<TestNinja> m​: class { has int $!n = 0; method x ($n) {$!n = $n} }.new.x​: 42
<camelia> rakudo-moar 2c95f7​: ( no output )

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

From @jnthn

On Thu Sep 15 11​:49​:35 2016, cpan@​zoffix.com wrote​:

#Doesn't work​:
<TestNinja> m​: class { has int $!n = 0; method x ($!n) {} }.new.x​: 42
<camelia> rakudo-moar 2c95f7​: OUTPUT«Cannot modify an immutable int␤
in method x at <tmp> line 1␤ in block <unit> at <tmp> line 1␤␤»

I've fixed this and added tests to S12-methods/attribute-params.t. It works for named parameters too. So in terms of the originally reported issue this ticket could be considered done.

But.

Unfortunately, the moment you have a role instead of a class, or a a more complex signature (for example, involving an unpack), it fails. So, some more work and tests needed.

From @usev6

For the records​: This fails on JVM (has to be fixed in src/vm/jvm/runtime/org/perl6/rakudo/Binder.java, probabaly)​:

$ ./perl6-j -e 'class { has int $!n = 0; method x ($!n) {} }.new.x​: 42'
org.perl6.nqp.sixmodel.reprs.P6OpaqueBaseInstance$BadReferenceRuntimeException​: Cannot access a native attribute as a reference attribute
  in method x at -e line 1
  in block <unit> at -e line 1

Tests that use the new method SeqNextNFromIterator fail due to this problem. From S32-list/head.t​:

$ ./perl6-j -e 'my $list = <a b b c>; say $list.head(3)'
org.perl6.nqp.sixmodel.reprs.P6OpaqueBaseInstance$BadReferenceRuntimeException​: Cannot access a native attribute as a reference attribute
  in block <unit> at -e line 1

This works, if one doesn't use a native here​: https://github.com/rakudo/rakudo/blob/2c681c55520d34750663cdec2fefcf3005ee550e/src/core/Rakudo/Internals.pm#L266

From @usev6

On Sat Oct 15 00​:31​:09 2016, bartolin@​gmx.de wrote​:

[...]
Tests that use the new method SeqNextNFromIterator fail due to this
problem. From S32-list/head.t​:

Again, for the records​: lizmat++ put in a bandaid for rakudo-j with Rakudo commit 666128fc6e. The tests from S32-list/head.t run fine, but the underlying problem is still there.

From @usev6

On Tue, 18 Oct 2016 08​:39​:21 -0700, bartolin@​gmx.de wrote​:

Again, for the records​: lizmat++ put in a bandaid for rakudo-j with
Rakudo commit 666128fc6e. The tests from S32-list/head.t run fine, but
the underlying problem is still there.

The bandaid was remove recently (Rakudo commit e8f938b0f6) after psch++ implemented attribute parameter binding on the JVM.

So we are back to what jnthn said about roles or more complex signatures​:

On Wed, 21 Sep 2016 06​:30​:00 -0700, jnthn@​jnthn.net wrote​:

I've fixed this and added tests to S12-methods/attribute-params.t. It
works for named parameters too. So in terms of the originally reported
issue this ticket could be considered done.

But.

Unfortunately, the moment you have a role instead of a class, or a a
more complex signature (for example, involving an unpack), it fails.
So, some more work and tests needed.