From john.haltiwanger@gmail.com

I encountered a consistent segfault while working out a trivial proxy
example in hopes of documenting the class.

How this might be condensed further is beyond me at the moment. After
removing the $!scrambler attribute, the code will no longer segfault, which
would defeat the purpose of this rakudobug.

Weirdly enough, if I remove $!string, it also stops segfaulting -- even
though it is never used. The name of the attribute doesn't seem to matter.

This class is modeled off of what I saw in the proxy-related spec tests.
The mutator test seems to do something very similar, but I haven't been
able to extend it.

## codeword.p6

class Codeword {
  has Sub $.scrambler is rw;
  has $!string;
  has $!encoded-string;

  submethod BUILD {
  my sub scrambler { $^s.trans​: 'a..mn..z' => 'n..za..m', :ii }
  $!scrambler = &scrambler;
  }

  method codeword returns Str is rw {
  return Proxy.new(
  FETCH => method () { $!encoded-string },
  STORE => method ($s) { $!encoded-string = $!scrambler($s) }
  );
  }
}

my $code = Codeword.new;
$code.codeword;

## perl6-debug-m output​:

+ proxy-test.p6 (23 - 25)
|
| my $code = Codeword.new;
| $code.codeword;

+ proxy-test.p6 (15 - 22)
|
| method codeword returns Str is rw {
| return Proxy.new(
| FETCH => method () { $!encoded-string },
| STORE => method ($s) { $!encoded-string = $!scrambler($s) }
| );
| }
| }

+ proxy-test.p6 (16 - 20)
| method codeword returns Str is rw {
| return Proxy.new(
| FETCH => method () { $!encoded-string },
| STORE => method ($s) { $!encoded-string = $!scrambler($s) }
| );

~/.rakudobrew/bin/perl6-debug-m​: line 2​: 14368 Segmentation fault​: 11
~/.rakudobrew/bin/../moar-HEAD/install/bin/perl6-debug-m "$@​"

From @ronaldxs

When I run this example now (Windows and Linux) I get​:

P6opaque​: no such attribute '$!encoded-string' on type Codeword in a Proxy when trying to get a value

instead of a segfault. If I tweak the code as below to use subs instead of methods for the Proxy hooks it runs fine. The P6opaque error seems reminiscent of a recent IRC conversation​: https://irclog.perlgeek.de/perl6/2018-03-03#i_15879434 . Between the IRC conversation and making it work by switching to subs I suspect it might be OK to merge this ticket with RT 126198 .

## codeword.p6

class Codeword {
  has Sub $.scrambler is rw;
  has $!string;
  has Str $!encoded-string;

  submethod BUILD {
  my sub scrambler { $^s.trans​: 'a..mn..z' => 'n..za..m', :ii }
  $!scrambler = &scrambler;
  }

  method codeword returns Str is rw {
  return Proxy.new(
  FETCH => sub ($) { $!encoded-string },
  STORE => sub ($,$s) { $!encoded-string = $!scrambler($s) }
  );
  }
}

my $code = Codeword.new;
$code.codeword;
$code.codeword = 'abc';
say $code.codeword;

prints
nop

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