From @dur-randir

The following two snippets result in 'Can't locate object method "foo" via package "G"' error, though they must succeed instead​:

*F​::foo = sub {};
*G​::ISA = ['H'];
$G​::ISA[0] = 'F';
G->foo;

===========

*F​::foo = sub {};
*G​::ISA = ['H'];
*G​::foo = ['H'];
*G​::ISA = *G​::foo;
$G​::ISA[0] = 'F';
G->foo;

The reason for this is that in glob_assign_glob and gv_setref only PERL_MAGIC_isa magic is assigned to the AV slot, but nothing to it's content. And PERL_MAGIC_isa -> PERL_MAGIC_isaelem propagation occurs only upon array write access, and not for individual elements' r/w access.

From @iabyn

On Sun, Jan 11, 2015 at 08​:19​:33AM -0800, Sergey Aleynikov wrote​:

# New Ticket Created by Sergey Aleynikov
# Please include the string​: [perl #123585]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=123585 >

The following two snippets result in 'Can't locate object method "foo" via package "G"' error, though they must succeed instead​:

*F​::foo = sub {};
*G​::ISA = ['H'];
$G​::ISA[0] = 'F';
G->foo;

===========

*F​::foo = sub {};
*G​::ISA = ['H'];
*G​::foo = ['H'];
*G​::ISA = *G​::foo;
$G​::ISA[0] = 'F';
G->foo;

The reason for this is that in glob_assign_glob and gv_setref only
PERL_MAGIC_isa magic is assigned to the AV slot, but nothing to it's
content. And PERL_MAGIC_isa -> PERL_MAGIC_isaelem propagation occurs
only upon array write access, and not for individual elements' r/w
access.

The first one was fixed by this​:

  commit 8452c1a
  Author​: Tony Cook <tony@​develop-help.com>
  Date​: Tue Jan 26 15​:53​:34 2016 +1100

  [perl #127351] add isaelem magic on *Foo​::ISA = arrayref

The second one still fails in blead.

--
The Enterprise is captured by a vastly superior alien intelligence which
does not put them on trial.
  -- Things That Never Happen in "Star Trek" #10

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